sensors
Article
Cross-Evaluation of Reflectivity from NEXRAD and Global
Precipitation Mission during Extreme Weather Events
Melisa Acosta-Coll 1, * , Abel Morales 2 , Ronald Zamora-Musa 3 and Shariq Aziz Butt 4
1
2
3
4
*
Citation: Acosta-Coll, M.; Morales,
A.; Zamora-Musa, R.; Butt, S.A.
Cross-Evaluation of Reflectivity from
NEXRAD and Global Precipitation
Mission during Extreme Weather
Events. Sensors 2022, 22, 5773.
https://doi.org/10.3390/s22155773
Academic Editors: Filippo Giannetti
and Luca Giovanni Lanza
Received: 15 June 2022
Accepted: 21 July 2022
Published: 2 August 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affiliations.
Department of Computer Science and Electronic, Universidad de la Costa, Barranquilla 080002, Colombia
Department of Electrical Engineering, University of Puerto Rico at Mayagüez,
Mayagüez, PR 00681-9018, USA; abel.morales@upr.edu
Department of Industrial Engineering, Universidad Cooperativa de Colombia UCC,
Barrancabermeja 687031, Colombia; ronald.zamora@campusucc.edu.co
Department of Computer Science, The University of Lahore, Lahore 54000, Pakistan; shariq2315@gmail.com
Correspondence: macosta10@cuc.edu.co
Abstract: During extreme events such as tropical cyclones, the precision of sensors used to sample the meteorological data is vital to feed weather and climate models for storm path forecasting,
quantitative precipitation estimation, and other atmospheric parameters. For this reason, periodic
data comparison between several sensors used to monitor these phenomena such as ground-based
and satellite instruments, must maintain a high degree of correlation in order to issue alerts with
an accuracy that allows for timely decision making. This study presents a cross-evaluation of the
radar reflectivity from the dual-frequency precipitation radar (DPR) onboard the Global Precipitation
Measurement Mission (GPM) and the U.S. National Weather Service (NWS) Next-Generation Radar
(NEXRAD) ground-based instrument located in the Caribbean island of Puerto Rico, USA, to determine the correlation degree between these two sensors’ measurements during extreme weather events
and normal precipitation events during 2015–2019. GPM at Ku-band and Ka-band and NEXRAD
at S-band overlapping scanning regions data of normal precipitation events during 2015–2019, and
the spiral rain bands of four extreme weather events, Irma (Category 5 Hurricane), Beryl (Tropical
Storm), Dorian (Category 1 hurricane), and Karen (Tropical Storm), were processed using the GPM
Ground Validation System (GVS). In both cases, data were classified and analyzed statistically, paying
particular attention to variables such as elevation angle mode and precipitation type (stratiform and
convective). Given that ground-based radar (GR) has better spatial and temporal resolution, the
NEXRAD was used as ground-truth. The results revealed that the correlation coefficient between
the data of both instruments during the analyzed extreme weather events was moderate to low;
for normal precipitation events, the correlation is lower than that of studies that compared GPM
and NEXRAD reflectivity located in other regions of the USA. Only Tropical Storm Karen obtained
similar results to other comparative studies in terms of the correlation coefficient. Furthermore, the
GR elevation angle and precipitation type have a substantial impact on how well the rain reflectivity
correlates between the two sensors. It was found that the Ku-band channel possesses the least bias
and variability when compared to the NEXRAD instrument’s reflectivity and should therefore be
considered more reliable for future tropical storm tracking and tropical region precipitation estimates
in regions with no NEXRAD coverage.
Keywords: cross-evaluation; reflectivity; NEXRAD; GPM; hurricane; ground validation system;
ground radar
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
1. Introduction
conditions of the Creative Commons
Hurricanes, or tropical cyclones (TC), are characterized by high-speed winds, heavy
precipitation, and low atmospheric pressure, that transform into natural disasters as they
reach land [1]. The major devastation occurs as a result of flooding [2,3]; therefore, rainfall
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Sensors 2022, 22, 5773. https://doi.org/10.3390/s22155773
https://www.mdpi.com/journal/sensors
Sensors 2022, 22, 5773
2 of 21
estimation is very important for emergency evacuation planning. When a hurricane
makes landfall, the most intense precipitation tends to occur in the vicinity of coastlines;
predicting this event is a significant operational challenge [4,5]. However, flooding due to
precipitation is not limited to coastlines, as seen in recent hurricanes where deadly floods
reached well inland.
The storm’s progression and resulting hazard effects on land are often highly uncertain.
Since the ensemble of forecasts changes during a TC, the uncertainty becomes dynamic,
and it only ends when the storm’s evolution is known completely [6,7]. In order to generate
a timely early warning system before and after the severe precipitation event, it is necessary
to have instruments with high accuracy for detection, measurement, and tracking of
storms [8].
A powerful instrument to monitor severe events such as tropical cyclones is the Global
Precipitation Measurement (GPM) mission, an international network of satellites used to
provide accurate and timely information. GPM is an international partnership sponsored by
NASA and the Japan Aerospace Exploration Agency (JAXA) that launched on 27 February
2014 [9]. This network can provide valuable information needed to monitor the evolution
of devastating storms, and helps scientists study their fast-moving and rapidly evolving
nature [10]. GPM carries two instruments: a passive microwave radiometer GMI and
a dual-frequency precipitation radar (DPR) [11]. The DPR consists of Ku-band (KuPR)
and Ka-band (KaPR) radars on the GPM spacecraft bus, which are capable of measuring
precipitation simultaneously [12]. These radars operate at frequencies of 13.91 GHz and
35.56 GHz, respectively, and provide a three-dimensional observation of rain with an
accurate estimation of rainfall rate. They are co-aligned and provide the same footprint
location on the earth of 5 km. KuPR is suitable for heavy rainfall in the tropical region, and
KaPR suitable for light rainfall in the higher latitude region [13]. DPR lower and upper
thresholds for rain rate measurements are 0.22 and 110.00 mm/h, respectively [14].
Ground-based weather radars, which provide a spatial resolution of 1 km or less, are
also used worldwide to detect and analyze rapidly moving severe storms, and to send
timely alerts to the community [15]. However, during severe and hazardous weather events,
these instruments can be damaged and consequently stop providing valid information; this
occurred when Hurricane Maria made landfall in Puerto Rico in 2017 and destroyed the
only NEXRAD on the island. Therefore, during severe weather events, it is vital to have
redundancy provided by satellite instruments in order to detect and monitor the events,
while ensuring the uninterrupted transmission of timely information [16].
When there are several instruments monitoring a weather event in the same region,
the information must be consistent between the instruments, especially for large areas
where hydrologic applications need information from multiple radar data. This information
is susceptible to radar measurement differences in the overlapping zones, due to radar
calibration, range effect, or both [16]. In order to mitigate this problem, NASA developed an
algorithm to match reflectivity from DPR and NEXRAD over different sampling volumes,
and this effort has been of great importance for evaluating and improving algorithm
performance [17].
One of the most affected U.S. territories during hurricane season in the Atlantic Ocean
is the island of Puerto Rico [18,19]. The most devastating hurricane that has impacted the
island was Hurricane Maria in September 2017; however, Hurricane Irma also impacted
Puerto Rico during that same month only 10 days earlier. Hurricane Irma was a category
5 hurricane with approximately 175-mile-per-hour winds, and was the strongest observed
in the Atlantic in terms of maximum sustained wind [20]. It lasted as a hurricane from 31
August until 11 September, and skirted the northeast region of Puerto Rico on 6 September
2017. This hurricane left more than 1 million people without electricity, some regions
without potable water, and damaged roads and communication system infrastructure in
Puerto Rico [21].
During Hurricane Irma, the NWS in Puerto Rico used weather satellites and a NEXRAD
radar to monitor the severe weather conditions. This radar is located in Cayey (18.12◦ N,
Sensors 2022, 22, 5773
3 of 21
66.08◦ W, 886.63 m elevation), is identified as TJUA, and operates at a frequency of 2.7 GHz
(S-Band). It has a maximum horizontal range of 462.5 km, and scans the entire island every
6 min with a spatial resolution of 1 km [22].
In 2018, the remnants of Tropical Storm Beryl affected Puerto Rico and the U.S. Virgin
Islands on 9 July. Strong winds and heavy rainfall affected Puerto Rico, where the average
rainfall ranged from 1 to 6 inches. Several locations reported flash flooding. As a consequence of this tropical storm, at least 24,000 homes and businesses were without electricity,
there were several fallen trees, and rivers rose over their banks; however, no injuries were
reported [1].
In September 2019, two extreme weather events hit Puerto Rico, Hurricane Dorian
in 6 September, and Tropical Storm Karen in 24–25 September. Dorian was the first major
hurricane of the 2019 Atlantic hurricane season. Although Dorian was less powerful
than Hurricanes Irma and Maria, people from Puerto Rico prepared for the worst since
they were still recovering from Maria. Fortunately, Hurricane Dorian’s projected path
unexpectedly swerved northward and left only some residents without electricity, and
some areas flooded.
Tropical Storm Karen became downgraded to a tropical depression when it hit Puerto
Rico. On its way through the island, flooding occurred and power outages affected less
than 10% of the total population.
This study presents an evaluation of GPM-DPR rainfall reflectivity against NEXRAD
TJUA radar reflectivity during four extreme weather events and during normal precipitation events, in order to determine the degree of correlation between these two instruments.
Measurement data from the extreme weather events in 2015–2019 were statistically analyzed, and reflectivity differences were broken down by precipitation type (stratiform and
convective) and radar elevation angle, comparing KaPR and KuPR with NEXRAD TJUA
separately.
The study results identified that the correlation coefficient between the data of both
instruments during the extreme weather events was moderate to low, and for normal
precipitation events the correlation is lower than that for other studies that compared GPM
and NEXRAD reflectivity located at other sites in the USA.
However, Tropical Storm Karen had a better correlation coefficient for its four angles
compared to the other extreme weather events. Likewise, the ground radar elevation
angle and precipitation type have a substantial impact on how well the reflectivities match,
and Ku-band possesses the least bias and variability when compared to ground radar
reflectivity.
Since extreme weather events are frequent in this area, it highlights the importance of
periodically conducting comparative studies to ensure consistency between instruments, in
order to provide high accuracy information that allows timely decision making.
The structure of this article is as follows: Section 2 presents a literature review of studies
that compare matched data from satellite-based radars and ground radars in different
regions of the globe. Section 3 describes the methodology, data, and procedures used to
carry out the cross-evaluation. Then, Section 4 presents the results and the discussion of
the cross-evaluation. Finally, Section 5 shows the conclusions of this research.
2. Literature Review
There have been multiple studies that compared that matched data between satellitebased radars and ground radars in different regions of the globe. The study developed
by [23] used space-borne precipitation radar information to quantitatively calibrate groundbased weather radar networks across China. Likewise, researchers from Colorado State University performed ground validation of GPM-DPR observations using an S-band NEXRAD
over the Dallas Fort Worth region in Texas, and reported that the reflectivities were well
matched. The intercomparison of reflectivity measurements between GPM-DPR and
NEXRAD radars carried out by researchers from NASA [24] found that taking samples
with narrow temporal gaps helps to reduce sample variability. Likewise, in order to reduce
‐
Sensors 2022, 22, 5773
4 of 21
‐
‐
the reflectivity differences among GRs in a similar environment, they suggest applying a
bias correction against the DPR. However, more studies are necessary in tropical regions,
and‐ it is also necessary to identify possible beam blockages that can affect patterns in the
GR intercomparison
results from before.
‐
‐
K. R. Morris and M. R. Schwaller from NASA performed a study of the sensitivity
of PR-GR measurements for constraints such as range from GR, minimum reflectivity
threshold, PR-GR time differences, and other variables. They found that there is a significant
‐
difference between PR and GR reflectivities in convective cases, particularly in convective
samples from the lower part of the atmosphere [25].
‐
‐
These studies have been deployed all over the world; nevertheless, there are relatively
‐
few that have been done for Latin America, especially the Caribbean. I. Arias and V.
‐
Chandrasekar performed a cross-validation of GPM with three GR radars from Colombia;
two C-band weather radars close to Bogota DC; and another one in San Andres Island
(Caribbean Ocean). The results showed that the Colombian radar and GPM observations
have a high correlation within 90%, and bias within 1 dBZ [26].
‐
3. Methodology
In order to obtain the matched data between GPM-DPR and NEXRAD during four
extreme weather events and during normal precipitation events, the data products available
‐
‐
from the GPM ground validation system (GVS)
validation network (VN) were used.
‐ The VN performs a direct match-up of DPR and GR data using the geometry-matching
algorithm developed by NASA from the GPM terrestrial validation system (GVS) [27].
The algorithm determines the intersection of individual DPR rays with each of the
‐
elevation sweeps of the circular scanning ground-based
radar, and the data outputs are
‐ ‐
stored as netCDF files. Due to the randomness of the beam-to-sweep
intersections, the
horizontal and vertical locations as well as the number of data points in the geometry
matching technique are different; moreover, this algorithm allows for the identification of
biases between ground observations and satellite recoveries. Figure 1 shows the geometric‐
intersections of DPR gates and GR sweeps at two different elevation angles.
Figure 1. GPM-DPR and ground radar geometric matching.
‐
The VN match-up data sets begins on 4 March 2014 (GMI) and 8 March 2014 (DPR,
Ka, Ku, DPRGMI), but the matched data with NEXRAD TJUA began in 2015.
In order to select the match-ups, only those gates at or above a specified rain rate or reflectivity threshold are included in the DPR and GR gate averages (variables DPR_dBZ_min,
GR_dBZ_min, and rain_min). These results are stored in netCDF variables [9].
‐
‐
‐
Sensors 2022, 22, 5773
5 of 21
‐
‐
‐
NEXRAD TJUA data and GPM Ku-band and Ka-band data for 2015 to 2019, in addition
to four extreme weather events that occurred in this same period of time, are compared in
terms of reflectivity differences for the first four matching elevation angles for the three
scanning modes for the GR, and categorized by precipitation type.
‐
The events for typical cases and for included extreme weather events cases do not
surpass the DPR upper threshold sensitivity rain rate of 110.00 mm/h. On average, crossmatching between DPR and GR over NEXRAD TJUA occurs every four days; occasionally,
‐
there can be two consecutive days with match data, and up to a week for a match to occur.
The average matching duration for GR and DPR is around 40 s, and DPR produces a swath
scan every 300 milliseconds. For this reason, DPR is not a good substitute for GR in terms
of continuous local weather monitoring; however, it is a useful instrument for GR data
calibration and validation, and is also useful in the absence of local GR, as was the case in
Puerto Rico after the damages suffered during Hurricane Maria.
GR has multiple scanning modes with different elevation angles, as Figure 2 shows.
Between 2015 and 2019, 165 cases with sufficient precipitation were selected for analysis, as
well as the four extreme weather events. Table 1 shows the selected elevation angles and
their corresponding beam heights.
(a)
(b)
(c)
Figure 2. NEXRAD elevation angle scanning modes of operation for (a) seven elevations, (b) eight
elevations and (c) nine elevations.
Table 1. Elevation angles and their maximum beam heights.
Angle
Maximum Beam Height (Km)
1
0.48◦
0.8377
2
1.31–1.45◦
2.53
3
2.42◦
4.22
4
3.125–3.39◦
5.91
‐ data within 100 km of the GR
The algorithm for the files used is V05A version 1.3, and
are used with a minimum threshold of 15 dBZ and a 7-km distance away from the GR.
‐
Each elevation angle is subcategorized by precipitation type, stratiform and convective;
then, the bias is calculated, in addition to the variance, mean absolute error (MAE), mean
square error (MSE), and root mean square (RMS), in order to determine variability in
reflectivity differences under the different categorizations and subcategorizations, number
of samples, and Pearson correlation coefficients (CC).
3.1. Extreme Weather Events
3.1.1. Hurricane Irma Data
Hurricane Irma’s eye passed north of Puerto Rico on 6 September by 8 p.m. as a
category 5 storm. By 4 a.m. on 7 September, it passed north of the Dominican Republic; consequently, this is a single event comparison between NEXRAD and GPM on 7
September 2017.
Sensors 2022, 22, 5773
6 of 21
‐‐
Figure 3a presents GOES East satellite image of the Caribbean at the moment when
Irma and GPM passed over PR on 7 September 2017; Figure 3b shows the map of Puerto
Rico with the ascending orbit of GPM over PR on 7 September 2017.
(a)
(b)
Figure 3. (a) GOES East satellite (7 September 2017); (b) map of Puerto Rico (7 September 2017).
3.1.2. Tropical Storm Beryl
Hurricane Beryl weakened to a tropical storm on Saturday, 7 July 2018 as it approached
‐‐
islands in the eastern Caribbean. In Puerto Rico, between 9 and 10 July strong winds were
reported; moreover, up to 8 inches of rain fell in some areas. Figure 4 shows Tropical Storm
Beryl over Puerto Rico.
Figure 4. Tropical Storm Beryl over Puerto Rico [28].
3.1.3. Hurricane Dorian
In Puerto Rico, along the east and southeast, between the 28th and 29th of August,
Hurricane Dorian left rainfall accumulations of between 4 and 6 inches, and generated
flash flooding especially across the eastern end of Puerto Rico. Figure 5 shows the closest
point between GPM and GR on 29 August at 7:01 pm local time (11:01 UTC).
Sensors 2022, 22, 5773
7 of 21
Figure 5. Hurricane Dorian over Puerto Rico [29].
3.1.4. Tropical Storm Karen
Tropical Storm Karen is the weakest event compared to the other three. Figure 6 shows
the image captured by the GPM’s core satellite when it passed over Tropical Storm Karen
on 25 September 2019 at 11:16 p.m. The most significant damages were heavy rains that led‐
to flooded roads, flash flood warnings, and hazardous marine conditions.
‐
Figure 6. Tropical Storm Karen [30].
The cross-evaluation
of the four extreme weather events (Irma, Beryl, Dorian, and
‐
Karen) follow the
‐ same categorization and analysis as the normal weather conditions cases
from the previous section; the biases were obtained, along with variances, mean absolute
errors (MAE), mean square errors (MSE), root mean square (RMS), and the correlation
coefficients for each GR elevation angle and subcategorized by precipitation type.
4. Results and Discussion
Data were analyzed and classified into normal weather conditions, which were the
data for 2015–2019 along with the four included extreme weather cases. Likewise, the
results were subcategorized by precipitation type for both cases, and calculated for bias,
variance, mean absolute error (MAE), mean square error (MSE), root mean square (RMS),
and the correlation coefficient between KuPR vs. NEXRAD TJUA and between KaPR vs.
NEXRAD TJUA.
Sensors 2022, 22, 5773
8 of 21
4.1. Normal Weather Conditions
Table 2 shows the statistical results for normal weather conditions.
Table 2. Statistical results for normal weather conditions.
Normal Weather Conditions
KuPR
Angle
KaPR
Stratiform
Convective
Stratiform
Convective
1
Bias
Variance
MAE
RMS
Samples
CC
−0.792329193
19.05459973
3.198405797
4.435640543
2548
0.707132246
−1.928060201
33.65576683
4.698553872
6.112789433
4816
0.695508443
−0.8233397
18.24078643
3.122685476
4.348742085
2563
0.701784846
−2.147966575
30.70512149
4.571603734
5.942434021
4828
0.690715355
2
Bias
Variance
MAE
RMS
Samples
CC
−0.643999145
19.95418399
3.224176468
4.512430194
2895
0.686310925
−1.959468715
32.30120898
4.611003214
6.01102083
3866
0.72902739
−0.771038608
19.10399729
3.163506815
4.437559084
2909
0.677008897
−2.230547626
29.52500261
4.510469111
5.873053157
3889
0.724902355
3
Bias
Variance
MAE
RMS
Samples
CC
−0.26332424
19.48338376
3.2547436
4.421061512
2808
0.671654104
−1.307805767
33.30169215
4.615509813
5.915974923
2506
0.704138687
−1.672383595
23.58685517
4.000603845
5.135681587
2776
0.570034514
−2.154162215
31.67090546
4.723886572
6.024842945
2516
0.680690284
4
Bias
Variance
MAE
RMS
Samples
CC
−0.26332424
19.48338376
3.2547436
4.421061512
2808
0.671654104
−1.307805767
33.30169215
4.615509813
5.915974923
2506
0.704138687
−1.852530874
20.68760321
3.842132901
4.910250175
2320
0.591936883
−2.493749553
30.70949712
4.788769913
6.075513292
1870
0.672371389
4.1.1. Angle 1 (0.4843◦ )
Figures 7–10 represent the scatter density plots for this case for GR angle 1 elevation
and the precipitation type.
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 1).
Figure 7. GPM-Ka
Sensors 2022, 22, 5773
9 of 21
‐
‐
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 1).
Figure 8. GPM-Ku
‐
‐
‐
‐
Figure 9. GPM-Ka
‐ vs. NEXRAD TJUA for convective precipitation (angle 1).
‐
‐
‐ vs. NEXRAD TJUA for convective precipitation (angle 1).
Figure 10. GPM-Ku
According to the statistical results for GR elevation angle 1 (0.4843◦ ) for normal
weather conditions, 77.5% of the samples correspond to convective precipitation, 22.5%
correspond to stratiform, and around 0.16% of the samples are categorized as other (their
precipitation types do not correspond to stratiform or convective). The means for KuPR
and KaPR show that there is better matching with GR data during stratiform precipitation.
However, the variance from KuPR is slightly more significant than KaPR. For both convective and stratiform precipitation, KuPR has better matching with GR data, as can be
compared with the scatter plots of Figures 8 and 10.
4.1.2. Angle 2 (1.45◦ )
Figures 11–14 represent the scatter density plots for this case for GR angle 2 elevation
and the precipitation type.
‐
Sensors 2022, 22, 5773
10 of 21
‐
‐
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 2).
Figure 11. GPM-Ka
‐
‐
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 2).
Figure 12. GPM-Ku
‐
‐
‐
‐
Figure 13. GPM-Ka vs. NEXRAD TJUA for convective precipitation (angle 2).
Sensors 2022, 22, 5773
11 of 21
‐
‐
‐ vs. NEXRAD TJUA for convective precipitation (angle 2).
Figure 14. GPM-Ku
For angle 2, the composition of the precipitation type is around 30% stratiform, 69.6%
convective, and 0.4% classified as other. The mean reflectivity difference for angle 2 has the
same behavior as angle 1, where KuPR has better matching for convective and stratiform
precipitation, although the mean reflectivity difference is lower for angle 1. Likewise, for
angle 2 the KuPR variance is more significant than it is for KaPR. Figures 12 and 14 illustrate‐
‐
that KuPR has better matching for convective and stratiform precipitation.
‐
4.1.3. Angle 3 (2.4219◦ )
Figures 15–18 represent the scatter density plots for this case for GR angle 3 elevation‐
‐
and the precipitation type.
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 3).
Figure 15. GPM-Ka
‐
‐
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 3).
Figure 16. GPM-Ku
‐
Sensors 2022, 22, 5773
12 of 21
‐
‐ vs. NEXRAD TJUA for convective precipitation (angle 3).
Figure 17. GPM-Ka
‐
‐
‐
‐ vs. NEXRAD TJUA for convective precipitation (angle 3).
Figure 18. GPM-Ku
The composition of the precipitation type for angle 3 is around 37.76% stratiform,
60.81% convective, and approximately 0.14% is classified as other. For GR angle 3, KuPR has
better matching for convective and stratiform precipitation, as shown in Figures 16 and 18.
Likewise, the variance is lower in KuPR for stratiform precipitation than it is for KaPR;
however, for convective precipitation it is the opposite, where KaPR has lower variance.
4.1.4. Angle 4 (3.125◦ )
Figures 19–22 represent the scatter density plots for this case for GR angle 4 elevation‐
‐
and the precipitation type.
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 4).
Figure 19. GPM-Ka
‐
‐
Sensors 2022, 22, 5773
13 of 21
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 4).
Figure 20. GPM-Ku
‐
‐
‐
‐ vs. NEXRAD TJUA for stratiform precipitation (angle 4).
Figure 21. GPM-Ka
‐
‐
‐
‐ vs. NEXRAD TJUA for convective precipitation (angle 4).
Figure 22. GPM-Ku
Finally, for normal weather conditions, the composition of the precipitation type‐‐
for angle 4 is around 42.54% stratiform, 53.71% convective, and approximately 3.75%‐
classified as other. The mean reflectivity difference from angle 4 shows that KuPR has
better correspondence with GR and lower variance than KaPR. For this angle, the stratiform
precipitation data are biased to GPM.
Sensors 2022, 22, 5773
14 of 21
4.2. Extreme Weather Conditions
This section presents the statistical results of the four extreme weather events, Hurricane Irma, Tropical Strom Beryl, Hurricane Dorian, and Tropical Storm Karen.
4.2.1. Hurricane Irma
Table 3 shows the statistical results for Hurricane Irma comparing the elevations angles
and the precipitation type.
Table 3. Statistical results for Hurricane Irma.
KuPR
KaPR
Angle
Statistics
Stratiform
Convective
Stratiform
Convective
1
Bias
Variance
samples
CC
MAE
MSE
RMS
−2.94313838
47.79819374
37
0.489350541
5.571226223
55.16841419
7.42754429
−2.821463626
17.01252891
46
0.816860184
3.859934019
24.60334832
4.960176239
−2.952524082
46.04521328
37
0.48798682
5.591467213
53.51814651
7.315609784
−2.850856449
16.73380946
46
0.819952168
3.824566883
24.49741349
4.949486184
2
Bias
Variance
Samples
CC
MAE
MSE
RMS
−2.555253983
49.33313154
40
0.491266891
5.765949059
54.62912617
7.391151884
−4.662028296
43.57828099
57
0.632773129
5.779512272
64.54825758
8.034193026
−2.508374166
47.92946176
40
0.490170722
5.725718832
53.02316618
7.281700775
−4.876060921
42.50447784
57
0.616068108
6.06207774
65.53475535
8.095353936
3
Bias
Variance
Samples
CC
MAE
MSE
RMS
−3.442076715
63.05476463
30
0.47654745
6.71135931
72.80083126
8.532340315
−4.692876602
55.53031483
49
0.530448225
6.653468521
76.4201339
8.741861009
−3.55133187
58.85108141
30
0.499089749
6.684085687
69.50133675
8.336746173
−5.081425375
51.8369617
49
0.501101383
6.683443537
76.59994836
8.752139645
4
Bias
Variance
Samples
CC
MAE
MSE
RMS
−3.487401009
52.35617101
26
0.51742935
6.236443079
62.50443792
7.905974824
−4.942844187
49.08833575
42
0.494104255
6.576980069
72.3512745
8.505955237
−4.157013245
44.4351132
25
0.569439427
6.208148499
59.93846779
7.741993786
−5.503968988
41.66927182
42
0.49362148
6.529815061
70.97082093
8.424418136
For GR angle 1 (0.4843◦ ) during Hurricane Irma, the precipitation type samples
are 44.58% stratiform and 55.42% convective, with no precipitation classified as other.
Comparing the biases for KuPR and KaPR, they are marginally better for convective
precipitation, while the variance for convective is less than half the values obtained for
the stratiform types. All precipitation types in angle 1 are also biased toward the GR;
in addition, convective type precipitation for Hurricane Irma has the best CC of all the
elevation angles.
For GR elevation angle 2 (1.31◦ ) for both Ku and Ka, the precipitation type samples
are 41.24% stratiform and 58.76% convective. In terms of the variance, angle 2 shows the
same behavior as angle 1, with the convective precipitation type being less than half the
values obtained for the stratiform types; in addition, angle 2 is biased toward GR. The bias
was better for the stratiform types, with Ka having less bias.
The statistical results for GR elevation angle 3 (2.42◦ ) for both Ku and Ka show that
the precipitation type samples are 37.97% stratiform and 62.03% convective, with no
precipitation classified as other. In terms of the bias, the behavior of angle 3 is similar to
Sensors 2022, 22, 5773
15 of 21
that of angle 2, in which Ka stratiform type has the least bias, followed by Ku convective;
however, only Ku convective type has a low variance compared to the other cases. All
precipitation types are biased toward GR.
For GR elevation angle 4 (3.125◦ ) for both Ku and Ka, the precipitation type samples
are 38.24% stratiform and 61.76% convective, with no precipitation classified as other. In
terms of the bias, the behavior is similar to that for angle 3; Ka stratiform type has the
least bias followed by Ku convective, with Ku convective type having the lowest variance
compared to the other cases. Overall, the bias values are worse for angle 4 than they are for
angle 3, and they are also all biased toward GR.
4.2.2. Tropical Storm Beryl
Table 4 presents the statistical results for Tropical Storm Beryl.
Table 4. Statistical results for Tropical Storm Beryl.
KuPR
KaPR
Angle
Statistics
Stratiform
Convective
Stratiform
Convective
1
Bias
Variance
Samples
CC
MAE
MSE
RMS
−4.188757324
29.69152265
30
0.417403818
4.995158386
46.24749315
6.800550944
−1.611068541
27.74995273
67
0.855086534
4.309867275
29.93131618
5.470952036
−4.119752185
27.92358558
30
0.416934835
4.804879443
43.96515745
6.630622705
−2.023071303
27.5691715
67
0.860353451
4.595677347
31.25050883
5.590215455
2
Bias
Variance
Samples
CC
MAE
MSE
RMS
−3.96698755
30.06729915
32
0.44173825
4.918266118
44.86468627
6.698110649
−3.094893278
27.45351222
59
0.82912417
4.777979673
36.56656286
6.047029259
−3.785002589
28.70518371
32
0.432862925
4.6668787
42.13439132
6.491100933
−3.461226754
25.46765433
59
0.82865775
5.012819953
37.01608981
6.084084961
3
Bias
Variance
Samples
CC
MAE
MSE
RMS
−2.309407976
28.40046399
27
0.529551794
4.490690726
32.68196015
5.716813811
−3.509221013
27.28209017
45
0.793626593
5.018928274
38.99045362
6.24423363
−2.604671902
30.59790247
27
0.49425288
4.659091243
36.24896254
6.020711132
−4.84570752
28.18860375
46
0.77078715
6.173538332
51.05668939
7.145396377
4
Bias
Variance
Samples
CC
MAE
MSE
RMS
−0.975679831
24.80327233
22
0.58487078
4.100157218
24.62780199
4.962640627
−3.669306331
11.49199802
36
0.875244005
4.201406161
24.63658481
4.963525441
−1.153117085
32.2660198
20
0.455514283
4.469336605
31.98239782
5.655298208
−6.505941709
15.71218863
36
0.760631905
6.817758348
57.60301647
7.589665109
For GR angle 1 (0.4843◦ ) during Beryl, the precipitation type samples are 30% stratiform and 67% convective, with 3% classified as other. As in the Hurricane Irma case, the
bias for KuPR and KaPR are better for convective precipitation. Likewise, convective type
precipitation has better CC than stratiform type, and it is also biased toward the GR [23].
For GR elevation angle 2 (1.31◦ ) for both Ku and Ka, the precipitation type samples
are 35% stratiform, 64% convective, and 1% for other types. Considering the bias, angle 2 is
biased toward GR. For this angle, the bias was better for the stratiform types, with the bias
for Ka being less, similar to the case for Hurricane Irma.
For the results of elevation angle 3 (2.42◦ ), the precipitation type sample distributions
are 36% stratiform and 61% convective, with 3% classified as other types. In terms of the
Sensors 2022, 22, 5773
16 of 21
bias, angle 3 is similar to angle 2 in which Ka stratiform type has the least bias followed by
Ku convective,
For GR elevation angle 4 (3.125◦ ), the precipitation type samples are 34% stratiform,
56% convective, and 8% classified as other, for Ku. For Ka, precipitation type samples are
34% stratiform, 62% convective, and 4% classified as other. In this angle, Ka stratiform type
has the least bias, followed by Ku convective; Ku convective type has the lowest variance
compared to the other cases.
4.2.3. Hurricane Dorian
Table 5 presents the statistical results for Hurricane Dorian.
Table 5. Statistical results for Hurricane Dorian.
KuPR
KaPR
Angle
Statistics
Stratiform
Convective
Stratiform
Convective
1
Bias
Variance
Samples
CC
MAE
MSE
RMS
−2.38389152
40.15040336
23
0.538710059
5.168910773
44.08767243
6.63985485
−4.20767755
68.38312472
36
0.473353709
7.117181645
84.18814384
9.175409737
−2.304239854
38.81483751
23
0.527199554
5.199398704
42.43675718
6.514350096
−4.658222198
62.83222884
36
0.443717362
7.266365634
82.7859232
9.098677003
2
Bias
Variance
Samples
CC
MAE
MSE
RMS
−2.28582089
30.76966538
27
0.683052459
4.381723439
34.85502529
5.903814469
−4.071136222
57.16153013
34
0.565677187
6.167973939
72.05445879
8.488489783
−2.137696407
30.67199076
27
0.679931993
4.437851553
34.10573703
5.840011732
−4.642113489
50.49311839
34
0.548841922
6.237545939
70.55724432
8.39983597
3
Bias
Variance
Samples
CC
MAE
MSE
RMS
−0.990524754
27.46570967
33
0.614723621
3.912260345
27.61455473
5.254955255
−2.85947046
56.70861986
31
0.552030308
5.906849984
63.05588085
7.940773316
−1.592194641
30.14648051
34
0.538029026
4.325223951
31.79490309
5.638696932
−3.820850403
47.42463277
31
0.5260822
5.536262543
60.49370371
7.777769842
4
Bias
Variance
Samples
CC
MAE
MSE
RMS
−0.813496431
22.36567372
36
0.62558895
3.372445424
22.40618145
4.733516817
−1.351946259
60.37829684
25
0.403635626
5.858706818
59.79092365
7.732459095
−1.90059691
25.97597365
36
0.523370099
3.999924898
28.86668744
5.372772789
−3.129214325
54.17977911
25
0.348124607
5.634678345
61.80457024
7.861588277
For GR angle 1 (0.4843◦ ) during Hurricane Dorian, the precipitation type samples are
39% stratiform and 61% convective, with no precipitation classified as other. The results for
this angle are similar to those for Hurricane Irma and Tropical Storm Beryl, in that both
precipitation types are biased toward the GR, and the convective type precipitation has a
better CC than stratiform type.
Similarly, angle 2 is biased toward GR like angle 1, but the bias was better for the
stratiform types. For both Ku and Ka, the precipitation type samples are 44.26% stratiform
and 58.76% convective.
The statistical results of GR elevation angle 3 (2.42◦ ) show that for both Ku and
Ka, the precipitation type samples are 37.97% stratiform and 55.73% convective, with no
precipitation classified as other. In terms of the bias, Ka stratiform type has the least bias
Sensors 2022, 22, 5773
17 of 21
followed by Ku convective; however, only Ku convective type has a low variance compared
to the other cases.
For GR elevation angle 4 (3.125◦ ) for both Ku and Ka, the precipitation type samples
are 59% stratiform and 41% convective, with no precipitation classified as other. The
variance is high for the four angles, but angle 4 presents a lower variance for the convective
precipitation. Likewise, the correlation coefficients are low, where KaPR has worse results,
especially for angle 4.
4.2.4. Tropical Storm Karen
Table 6 shows the statistical results for Tropical Storm Karen.
Table 6. Statistical results for Tropical Storm Karen.
KuPR
KaPR
Angle
Statistics
Stratiform
Convective
Stratiform
Convective
1
Bias
Variance
samples
CC
MAE
MSE
RMS
−1.5556556
8.672564753
71
0.86673526
2.370126778
10.9704803
3.312171539
1.706651317
8.106865581
36
0.937141932
2.555990166
10.79433359
3.285473115
−1.806369029
9.316739678
71
0.837512015
2.527218563
12.44848706
3.528241356
−0.793639024
2.46326481
36
0.934651891
1.31192202
3.024703688
1.739167527
2
Bias
Variance
Samples
CC
MAE
MSE
RMS
−0.602297948
5.857037297
75
0.903787903
1.889265315
6.141706285
2.478246615
1.480800735
6.640760467
36
0.930935096
2.223025746
8.649065714
2.940929396
−0.815835025
6.034862038
75
0.876159423
1.974323667
6.619983998
2.572932956
−0.150544167
2.335265974
36
0.946492355
1.189369731
2.293061021
1.514285647
3
Bias
Variance
Samples
CC
MAE
MSE
RMS
0.801119123
6.242063048
84
0.874454055
2.126662118
6.809544623
2.609510418
2.871341123
6.562596797
36
0.877279437
3.117811468
14.62490228
3.824251859
−2.132589764
5.661498234
81
0.844826152
2.542521371
10.1395423
3.184264797
0.06831736
4.379294642
36
0.887496647
1.659194893
4.26231483
2.064537437
4
Bias
Variance
Samples
CC
MAE
MSE
RMS
2.092964198
2.919875752
75
0.891335296
2.362140477
7.261443209
2.694706516
2.910401053
5.280831345
36
0.89085389
3.095258633
13.60457587
3.688438135
−1.220398197
4.885140215
73
0.795730659
1.825778844
6.307592247
2.511492036
−1.353463411
3.443681709
36
0.908970434
1.951402744
5.17988709
2.27593653
Tropical storm Karen is the weakest of the previous extreme events, and unlike the
others with similar behaviors for the first three angles, the results obtained for this event
are different. The first place for the convective type of KuPR in all four angles is biased to
GPM. On the other hand, for stratiform precipitation, angles 1 and 2 of KuPR are biased to
GR, while angles 3 and 4 are biased to GPM. Considering the CCs for angles 1 and 2, the
CCs are higher for KuPR; however, for angles 3 and 4 the CCs are slightly better for KaPR.
Comparing the results of normal weather cases with the four extreme weather events,
there is better correspondence in the results obtained for cases between 2015 and 2019,
this in part due to the fact that there are many more samples. According to the statistical
analysis and scatter density plots, for normal weather cases the reflectivity difference for
every case is biased toward the GR except for angle 4 Ku-band and the stratiform case.
Likewise, Ku-band has the best matching in every case for the stratiform and convective
Sensors 2022, 22, 5773
18 of 21
cases. For the Hurricane Irma case, the mean reflectivity difference is biased toward the GR
(negative bias) for each elevation angle of the GR, and also for each GPM band. The first
elevation angles (0.48 and 1.31 degrees) show better matching than the values obtained
for angles 3 and 4 (2.42 and 3.125 degrees) in terms of the mean reflectivity difference
and variance.
Concerning the precipitation type, convective precipitation shows less variability
compared to the stratiform precipitation in Ku-band and Ka-band. For the elevation angle,
Ku-band shows substantially less variability in the higher elevation angles when compared
to Ka-band. On the other hand, during normal weather conditions, an elevation angle for
GR of around 3.39 degrees gives the best matching in terms of bias, variability, and CC; for
the case of Hurricane Irma, an elevation angle of 0.48 degrees offers better results.
Of significance is that Hurricane Irma, Tropical Storm Beryl, and Hurricane Dorian
showed lower biases and variances for precipitation classified as convective when compared to stratiform for DPR-Ku; likewise, most cases exceeded 5 dBZ and were highly
variable except for convective type precipitation. For the cases in 2015–2019, stratiform
precipitation generally showed lower values of bias than the convective type.
Regarding the correlation coefficient (CC), for normal weather cases and stratiform
precipitation, the CCs for KuPR are between 0.67 and 0.70, and for KaPR they are 0.57–0.70.
Likewise, for convective precipitation, the CCs for KuPR are 0.69–0.70 and for KaPR they
are 0.67–0.72. These CCs are much lower compared to the results obtained in the study
carried out by [20], which quantitatively compared GPM’s observations of reflectivity with
instantaneous rainfall products of five NEXRAD ground radars located in the southeastern
plains of the U.S.A. Table 7 shows the correlation coefficients obtained by [20] classified
into precipitation type.
Table 7. Correlation coefficients for DPR Ku-band and Ka-band reflectivity vs. NEXRAD S-band
reflectivity [20].
KuPR
Nexrad Radar
KFWS (Dallas/Ft. Worth, TX, USA)
KHGX (Houston/Galveston, TX, USA)
KSHV (Shreveport, LA, USA)
KLIX(New Orleans, LA, USA)
KMLB (Melbourne, FL, USA)
KaPR
Stratiform (CC)
Convective (CC)
Stratiform (CC)
Convective (CC)
0.89
0.88
0.90
0.89
0.83
0.88
0.89
0.85
0.84
0.86
0.82
0.78
0.82
0.79
0.66
0.82
0.83
0.80
0.76
0.71
For the Hurricane Irma case, the CCs for stratiform precipitation are between 0.4765
and 0.5174 for KuPR and between 0.4880 and 0.5807 for KaPR. For convective precipitation,
the CCs for KuPR range from 0.4941 to 0.8169 and for KaPR the CCs are 0.4936–0.8200,
where the higher values are from angle 1.
The CC range for Tropical Storm Beryl related to stratiform precipitation is between
0.417 and 0.584 for KuPR, and 0.416–0.494 for KaPR. For convective precipitation, the CCs
are significantly higher than those for stratiform type, since the CCs for KuPR range from
0.79 to 0.87, while for KaPR they are 0.76–0.86, where the higher values are from angle 1.
On the other hand, Hurricane Dorian exhibited similar behavior to Hurricane Irma.
The CCs for stratiform precipitation are between 0.53 and 0.68 for KuPR, and between
0.52 and 0.67 for KaPR; these values are slightly better than those for Hurricane Irma. For
convective precipitation, the CCs for KuPR range from 0.40 to 0.55, and for KaPR are from
0.34 to 0.54; they are significantly lower than the corresponding CCs for Hurricane Irma
and Tropical Storm Beryl.
Finally, the CCs for Tropical Storm Karen are the greatest of the four extreme weather
events for both cases, stratiform and convective precipitation types. The CCs for stratiform
precipitation are between 0.86 and 0.90 for KuPR, and between 0.79 and 0.94 for KaPR;
Sensors 2022, 22, 5773
19 of 21
these values are slightly better than those corresponding to Hurricane Irma. For convective
precipitation, the CCs for KuPR range from 0.87 to 0.93, and for KaPR are from 0.88 to 0.94.
These results indicate that it is necessary to apply corrective algorithms in order to
improve the calibration of the GR located in Puerto Rico, and to increase the correlation
of the data between GR and GPM. As the event becomes more extreme, the correlation
coefficient decreases. Implementing corrective algorithms is a necessary action, considering
that the GR is the main instrument used by the government of this country to design
forecasts and issue alerts to the community.
5. Conclusions
This study performed a cross-evaluation of reflectivity from GPM-DPRs for both Kuand Ka-band against the ground-based radar NEXRAD located in Puerto Rico (TJUA),
for two cases: during normal weather precipitation events and during four extreme
weather events.
Data from TJUA in 2015–2019 (normal precipitation cases) and from the extreme
weather events were compared in terms of biases and correlation coefficients, and used
the first four matching elevation angles for the three scanning modes of the GR, and
subsequently categorized by the type of precipitation (stratiform and convective).
The statistical analysis shows that Ku-band possesses the least bias and variability
when compared to ground radar reflectivity; for this reason, DPR-Ku is better suited for
reflectivity measurements in normal to moderate weather conditions in the Caribbean
Region close to Puerto Rico.
Furthermore, the results showed that the elevation angle of the GR has a strong impact
in how well the reflectivities match. Likewise, an elevation angle of 3.39 degrees was
determined as the best to use for DPR-Ku in normal weather conditions, while for a severe
event such as Hurricane Irma, a lower elevation angle such as 0.4843 degrees has the best
matching for DPR-Ku and Ka.
The precipitation type also has a significant impact on how well matched the GR and
DPR data are. For normal weather precipitation conditions, the stratiform type is statistically better for every GR elevation angle in comparison to the convective type. Similarly,
when there are a lower number of convective types samples, the matching is improved, as
is the case when the GR elevation angle is higher. Similarly, for Hurricane Irma, Tropical
Storm Beryl, and Hurricane Dorian, the precipitation type also had a substantial impact
on DPR-GR matching, with a lower GR elevation angle and convective type offering the
best match.
However, in terms of the correlation coefficients for both cases, normal weather
precipitation conditions and three of the extreme events (Hurricane Irma, Tropical Strom
Beryl, and Hurricane Dorian), the results are lower than those from other studies that
compared GPM-DPR observations with different NEXRAD locations in the U.S.A; therefore,
it is necessary to apply corrective algorithms in order to improve the calibration of the GR
located in Puerto Rico. It is necessary to increase the correlation of the data between GR
and GPM so that they can provide accurate information for both rain events under normal
conditions, and for severe events such as during tropical cyclones.
Author Contributions: Formal analysis, M.A.-C.; Funding acquisition, A.M.; Investigation, M.A.-C.,
R.Z.-M. and S.A.B.; Methodology, A.M. All authors have read and agreed to the published version of
the manuscript.
Funding: The APC was funded by Universidad Cooperativa de Colombia (Barrancabermeja, Colombia).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
Sensors 2022, 22, 5773
20 of 21
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
de Beurs, K.M.; McThompson, N.S.; Owsley, B.C.; Henebry, G.M. Hurricane damage detection on four major Caribbean islands.
Remote Sens. Environ. 2019, 229, 1–13. [CrossRef]
NSF and The University of Rhode Island. Rainfall and Inland Flooding. 2010. Available online: http://hurricanescience.org/
society/impacts/rainfallandinlandflooding/ (accessed on 20 October 2021).
Ortega-Gonzalez, L.; Acosta-Coll, M.; Piñeres-Espitia, G.; Butt, S.A. Communication protocols evaluation for a wireless rainfall
monitoring network in an urban area. Heliyon 2021, 18, 7. [CrossRef] [PubMed]
Ren, Y.; Zhang, J.; Guimond, S.; Wang, X. Hurricane Boundary Layer Height Relative to Storm Motion from GPS Dropsonde
Composites. Atmposphere 2019, 10, 339. [CrossRef]
Trepanier, J. North Atlantic Hurricane Winds in Warmer than Normal Seas. Atmposphere 2020, 11, 293. [CrossRef]
Yang, K.; Davidson, R.A.; Blanton, B.; Colle, B.; Dresback, K.; Kolar, R.; Nozick, L.K.; Trivedi, J.; Wachtendorf, T. Hurricane
evacuations in the face of uncertainty: Use of integrated models to support robust, adaptive, and repeated decision-making. Int. J.
Disaster Risk Reduct. 2019, 36, 101093. [CrossRef]
Luitel, B.; Villarini, G.; Vecchi, G. Verification of the skill of numerical weather prediction models in forecasting rainfall from U.S.
landfalling tropical cyclones. J. Hydrol. 2018, 556, 1026–1037. [CrossRef]
Ramirez-Cerpa, E.; Acosta-Coll, M.; Velez-Zapata, J. Analysis of the climatic conditions for short-term precipitation in urban
areas: A case study Barranquilla, Colombia. Idesia 2017, 35, 2. [CrossRef]
Neeck, S.P.; Kakar, R.K.; Azarbarzin, A.A.; Hou, A.Y. Global Precipitation Measurement (GPM) launch, commissioning, and early
operations. Sens. Syst. Next-Gener. Satell. XVIII 2014, 9241, 31–44. [CrossRef]
Omranian, E.; Sharif, H.O.; Tavakoly, A.A. How Well Can Global Precipitation Measurement (GPM) Capture Hurricanes? Case
Study: Hurricane Harvey. Remote Sens. 2018, 10, 1150. [CrossRef]
Furukawa, K.; Yamamoto, K.; Kubota, T.; Oki, R.; Iguchi, T. Current status of the Dual-frequency precipitation Radar on the
Global Precipitation Measurement core spacecraft and scan pattern change test operations results. Remote Sens. Atmos. Clouds
Precip. VII 2018, 10776, 1077602. [CrossRef]
Hou, A.Y.; Kakar, R.K.; Neeck, S.; Azarbarzin, A.A.; Kummerow, C.D.; Kojima, M.; Oki, R.; Nakamura, K.; Iguchi, T. The
Global Precipitation Measurement Mission; American Metereological Society: Boston, MA, USA, 2014. Available online: https:
//pdfs.semanticscholar.org/c2c9/e1aca77adaf560d24f08ca72e58b4484e66d.pdf (accessed on 9 August 2021).
Skofronick-Jackson, G.; Petersen, W.A.; Berg, W.; Kidd, C.; Stocker, E.F.; Kirschbaum, D.B.; Kakar, R.; Braun, S.A.; Huffman, G.J.;
Iguchi, T.; et al. The Global Precipitation Measurement (GPM) Mission for Science and Society. Bull. Am. Meteorol. Soc. 2017, 98,
1679–1695. [CrossRef] [PubMed]
Baldini, L.; Roberto, N.; Montopoli, M.; Adirosi, E. Ground-Based Weather Radar to Investigate Thunderstorms. In Remote Sensing
of Clouds and Precipitation; Springer: Cham, Switzerland, 2018; pp. 113–135. [CrossRef]
Acosta-Coll, M.; Ballester-Merelo, F.; de la Hoz-Franco, E.; Martinez-Peiró, M. Real-time early warning system design for pluvial
flash floods—A review. Sensors 2018, 18, 2255. [CrossRef] [PubMed]
Keem, M.; Seo, B.C.; Krajewski, W.F.; Morris, K.R. Intercomparison of Reflectivity Measurements between GPM DPR and
NEXRAD Radars. Atmos. Res. 2019, 226, 49–65. [CrossRef]
Biswas, S.; Chandrasekar, V. Cross-Validation of Observations between the GPM Dual-Frequency Precipitation Radar and Ground
Based Dual-Polarization Radars. Remote Sens. 2018, 10, 1773. [CrossRef]
Kim, K.; Bui, L. Learning from Hurricane Maria: Island ports and supply chain resilience. Int. J. Disaster Risk Reduct. 2019,
39, 101244. [CrossRef]
López-Marrero, T.; Castro-Rivera, A. Let’s not forget about non-land-falling cyclones: Tendencies and impacts in Puerto Rico. Nat.
Hazards 2019, 98, 809–815. [CrossRef]
Bacopoulos, P. Extreme low and high waters due to a large and powerful tropical cyclone: Hurricane Irma (2017). Nat. Hazards
2019, 98, 3. [CrossRef]
Benach, J.; Diaz, M.R.; Muñoz, N.J.; Martinez-Herera, E.; Pericas, J.M. What the Puerto Rican hurricanes make visible: Chronicle
of a public health disaster foretold. Soc. Sci. Med. 2019, 238, 112367. [CrossRef] [PubMed]
Colom, J.G.; Cruz-Pol, S.; Pablos, G.; Córdoba, M.F.; Castellanos, W.; Acosta, M.; Ortiz, J.A.; de Jesús, B.; Trabal, J. Uprm Weather
Radars at the Central American and Caribbean Games at Mayagüez 2010. IEEE Geosci. Remote Sens. Lett. 2010, 156, 34–39.
Zhong, L.; Yang, R.; Wen, Y.; Chen, L.; Gou, Y.; Li, R.; Zhou, Q.; Hong, Y. Cross-evaluation of reflectivity from the space-borne
precipitation radar and multi-type ground-based weather radar network in China. Atmos. Res. 2017, 196, 200–210. [CrossRef]
Morris, K.R.; Greenbelt, S.; Schwaller, M.R. Sensitivity of Spaceborne and Ground Radar Comparison Results to Data Analysis
Methods and Constraints. In Proceedings of the 35th Conference on Radar Meteorology, Pittsburgh, PA, USA, 26–30 September
2011. Available online: https://ams.confex.com/ams/35Radar/webprogram/Paper191729.html (accessed on 5 July 2021).
Biswas, S.K.; Chandrasekar, V. Cross validation of observations from GPM dual-frequnecy precipitation radar with S-band
ground radar measurents over the Dallas—Fort worth region. In Proceedings of the 2017 IEEE International Geoscience and
Remote Sensing Symposium (IGARSS), Fort Worth, TX, USA, 23–28 July 2017; pp. 2085–2088. [CrossRef]
Arias, I.; Chandrasekar, V. Cross Validation of GPM and Ground-Based Radar in Latin America and the Caribbean. In Proceedings
of the IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain, 22–27 July 2018;
pp. 3891–3893. [CrossRef]
Sensors 2022, 22, 5773
27.
28.
29.
30.
21 of 21
Goddard Space Flight Center. Global Precipitation Mission (GPM) Ground Validation System Validation Network Data Product
User’s Guide. 2013. Available online: https://gpm.nasa.gov/sites/default/files/document_files/Val_Network_Users_Guide_v4
.1.pdf (accessed on 9 June 2021).
National Hurricane Center. Hurrican Beryl. Available online: https://www.nhc.noaa.gov/data/tcr/AL022018_Beryl.pdf
(accessed on 6 June 2021).
National Weather Service. Hurricane Dorian. 2019. Available online: https://www.weather.gov/mhx/Dorian2019 (accessed on 6
June 2021).
National Weather Service. Tropical Storm Karen. 2019. Available online: https://www.weather.gov/sju/karen2019 (accessed on
6 June 2021).