Information about glacier volume and ice thickness distribution is essential for many glaciologic... more Information about glacier volume and ice thickness distribution is essential for many glaciological applications, but direct measurements of ice thickness can be difficult and costly. We present a new method that calculates ice thickness via an estimate of ice flux. We solve the familiar continuity equation between adjacent flowlines, which decreases the computational time required compared to a solution on the whole grid. We test the method on Columbia Glacier, a large tidewater glacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results. This shows the potential of this method for estimating ice thickness distribution of glaciers for which only surface data are available. We find that both the mean thickness and volume of Columbia Glacier were approximately halved over the period 1957–2007, from 281 m to 143 m, and from 294 km3 to 134 km3, respectively. Using bedrock slope and considering how waves of thickness change propagate through the g...
The San Joaquin Valley is identified as an area with a high level of particulate matter (PM) in t... more The San Joaquin Valley is identified as an area with a high level of particulate matter (PM) in the air, reaching above the federal and state clean air standards (EPA 2019). Many of the cities in the valley are classified as the most polluted cities in the United States for both particulate matter and ozone pollution (American Lung Association, 2021). To resolve this issue, alternative forms of transportation have been considered in transportation planning. In this study, active transportation mode air quality was monitored on selected Woodward Park and Old Clovis trails and urban bike lanes. Real-time aerosol monitors, and low-cost sensors were carried in a backpack on bicycles during the sampling. Researchers collected GPS data via a portable GPS technology called Tracksticks. Driving transportation mode air quality data was acquired from the roadways within the Fresno/Clovis area, spanning six sampling routes, and during intercity trips between Fresno, Berkeley, and Los Angeles, ...
To promote active transportation modes (such as bike ride and walking), and to create safer commu... more To promote active transportation modes (such as bike ride and walking), and to create safer communities for easier access to transit, it is essential to provide consolidated data-driven transportation information to the public. The relevant and timely information from data facilitates the improvement of decision-making processes for the establishment of public policy and urban planning for sustainable growth, and for promoting public health in the region. For the characterization of the spatial variation of transportation-emitted air pollution in the Fresno/Clovis neighborhood in California, various species of particulate matters emitted from traffic sources were measured using real-time monitors and GPS loggers at over 100 neighborhood walking routes within 58 census tracts from the previous research, Children’s Health to Air Pollution Study - San Joaquin Valley (CHAPS-SJV). Roadside air pollution data show that PM2.5, black carbon, and PAHs were significantly elevated in the neigh...
Point cloud data from laser scanner has a complementary property to imagery data such as surface ... more Point cloud data from laser scanner has a complementary property to imagery data such as surface information vs. texture information. Advance in technology has reached to the point where a camera mounted on top of a laser scanner can assign color directly from image pixels to 3D point clouds. Current terrestrial laser scanning system with camera on board uses digital image pixel (color) retrieval and Orthophoto generation, but the scanner camera is not fully utilized in terms of 3-dimensional measurement. For example, a target that is more than 100 meters from the system tends to experience a degraded image, spatial resolution-wise, while generating a sufficient number of points. It simply means image resolution is fixed while laser-scanning parameters are adjustable through scan rate, scan angle etc. The objective of this study is to incorporate a high-resolution imaging system to the laser scanning system so that color information is updated from high-resolution image.
Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a r... more Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a rapid and complex response to external forcing. Despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along Greenland's northwestern margin, it is unclear whether west Greenland glaciers have undergone the synchronous speed-up and subsequent slow-down as observed in southeastern glaciers earlier in the decade. To investigate changes in west Greenland outlet glacier dynamics and the potential controls behind their behavior, we derive time series of front position, surface elevation, and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west Greenland from 2000 to 2009. Using these data, we look for relationships between retreat, thinning, acceleration, and geometric parameters to determine the first-order controls on glacier behavior. Our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales, though nearly all glaciers retreated and thinned over the decade. We found no direct relationship between retreat, acceleration, and external forcing applicable to the entire region. In regard to geometry, we found that, following retreat, (1) glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and (2) thinning rates declined more quickly for glaciers with steeper slopes. Overall, glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front, but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west Greenland.
Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakob... more Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakobshavn Isbræ, accounted for a substantial portion of the ice sheet's mass loss over the past decade. Rapid changes in their discharge, however, make their cumulative mass-change uncertain. We derive monthly mass balance rates and cumulative balance from discharge and surface mass balance (SMB) rates for these glaciers from 2000 through 2010. Despite the dramatic changes observed at Helheim, the glacier gained mass over the period, due primarily to the short duration of acceleration and a likely longer-term positive balance. In contrast, Jakobshavn Isbræ lost an equivalent of over 11 times the average annual SMB and loss continues to accelerate. Kangerdlugssuaq lost over 7 times its annual average SMB, but loss has returned to the 2000 rate. These differences point to contrasts in the long-term evolution of these glaciers and the danger in basing predictions on extrapolations of recent changes.
This article evaluates UAV photogrammetry systems using smartphones and smart cameras. Image tria... more This article evaluates UAV photogrammetry systems using smartphones and smart cameras. Image triangulation was conducted in accordance with interior orientation parameters, determined by camera self-calibration. Precise orthomosaic images and digital surface models were generated, and their accuracy was assessed using aerial and terrestrial lidar data. Digital surface models were used to estimate earthwork volumes and verify the suitability of UAV photogrammetry for use on construction sites. Georeferencing accuracy shows that the smart camera performs about twice as well as the smartphone with reference to checkpoints and polygon parts. Considering rolling shutter in the smartphone, it is possible to increase accuracy. Especially in inclined and rugged topography, the smartphone can benefit from applying the rolling-shutter method. Earthwork of volume error is often applied as a legal requirement for some countries, and our findings indicate that a smart camera with a drone can be ...
Geografiska Annaler: Series A, Physical Geography, 2017
ABSTRACT To estimate hydrological storage and better understand the climatic implications of glac... more ABSTRACT To estimate hydrological storage and better understand the climatic implications of glacier retreat, the volume of glacial ice is a critical but problematic variable. High-accuracy mapping of glacier surface changes over time can directly estimate volume changes, allowing for explicit testing and refining of scaling relationships between changes in glacier volume and surface area that are necessary for making an inventory of remaining glacier mass with remote imagery. A combination of airborne LiDAR, spaceborne remote sensing imagery, digital photogrammetry, and geospatial techniques is used to assess the changes in volume and surface area of six glaciers in the Cordillera Blanca, Peru, between 1962 and 2008. The loss of glacier surface area ranges from 30.79% to 72.62%, corresponding to individual glacier volume changes ranging from 0.019 to 0.150 km3. The volume–surface area scaling is deduced from the change in volume related to the change in surface area by a power relationship quantified from 13 different epoch series. The result shows that there is about 36% more volume loss relative to the loss expected from surface area alone of these individual glaciers in the study area than other glaciers in mid- and high-latitudes from the previous study. Since the error of volume estimation shows a much larger impact on the increase with the size of glaciers, volume–surface area scaling analysis needs to include larger ice masses with regional inventories for a more accurate estimation.
Evaluating the historical contribution of the volume loss of ice to stream flow based on reconstr... more Evaluating the historical contribution of the volume loss of ice to stream flow based on reconstructed volume changes through the Little Ice Age (LIA) can be directly related to the understanding of glacier-hydrology in the current epoch of rapid glacier loss that has disquieting implications for a water resource in the Cordillera Blanca in the Peruvian Andes. However, the accurate prediction of the future glacial meltwater availability for the developing regional Andean society needs more extensive quantitative estimation from long-term glacial meltwater of reconstructed glacial volume. Modeling the LIA paleoglaciers through the mid-19th century (with the most extensive recent period of mountain glacier expansion having occurred around 1850 AD) in different catchments of the Cordillera Blanca allows us to reconstruct glacier volume and its change from likely combinations of climatic control variables and time. We computed the rate and magnitude of centennial-scale glacier volume ch...
Information about glacier volume and ice thickness distribution is essential for many glaciologic... more Information about glacier volume and ice thickness distribution is essential for many glaciological applications, but direct measurements of ice thickness can be difficult and costly. We present a new method that calculates ice thickness via an estimate of ice flux. We solve the familiar continuity equation between adjacent flowlines, which decreases the computational time required compared to a solution on the whole grid. We test the method on Columbia Glacier, a large tidewater glacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results. This shows the potential of this method for estimating ice thickness distribution of glaciers for which only surface data are available. We find that both the mean thickness and volume of Columbia Glacier were approximately halved over the period 1957–2007, from 281 m to 143 m, and from 294 km3 to 134 km3, respectively. Using bedrock slope and considering how waves of thickness change propagate through the g...
The San Joaquin Valley is identified as an area with a high level of particulate matter (PM) in t... more The San Joaquin Valley is identified as an area with a high level of particulate matter (PM) in the air, reaching above the federal and state clean air standards (EPA 2019). Many of the cities in the valley are classified as the most polluted cities in the United States for both particulate matter and ozone pollution (American Lung Association, 2021). To resolve this issue, alternative forms of transportation have been considered in transportation planning. In this study, active transportation mode air quality was monitored on selected Woodward Park and Old Clovis trails and urban bike lanes. Real-time aerosol monitors, and low-cost sensors were carried in a backpack on bicycles during the sampling. Researchers collected GPS data via a portable GPS technology called Tracksticks. Driving transportation mode air quality data was acquired from the roadways within the Fresno/Clovis area, spanning six sampling routes, and during intercity trips between Fresno, Berkeley, and Los Angeles, ...
To promote active transportation modes (such as bike ride and walking), and to create safer commu... more To promote active transportation modes (such as bike ride and walking), and to create safer communities for easier access to transit, it is essential to provide consolidated data-driven transportation information to the public. The relevant and timely information from data facilitates the improvement of decision-making processes for the establishment of public policy and urban planning for sustainable growth, and for promoting public health in the region. For the characterization of the spatial variation of transportation-emitted air pollution in the Fresno/Clovis neighborhood in California, various species of particulate matters emitted from traffic sources were measured using real-time monitors and GPS loggers at over 100 neighborhood walking routes within 58 census tracts from the previous research, Children’s Health to Air Pollution Study - San Joaquin Valley (CHAPS-SJV). Roadside air pollution data show that PM2.5, black carbon, and PAHs were significantly elevated in the neigh...
Point cloud data from laser scanner has a complementary property to imagery data such as surface ... more Point cloud data from laser scanner has a complementary property to imagery data such as surface information vs. texture information. Advance in technology has reached to the point where a camera mounted on top of a laser scanner can assign color directly from image pixels to 3D point clouds. Current terrestrial laser scanning system with camera on board uses digital image pixel (color) retrieval and Orthophoto generation, but the scanner camera is not fully utilized in terms of 3-dimensional measurement. For example, a target that is more than 100 meters from the system tends to experience a degraded image, spatial resolution-wise, while generating a sufficient number of points. It simply means image resolution is fixed while laser-scanning parameters are adjustable through scan rate, scan angle etc. The objective of this study is to incorporate a high-resolution imaging system to the laser scanning system so that color information is updated from high-resolution image.
Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a r... more Recent changes in the dynamics of Greenland's marine terminating outlet glaciers indicate a rapid and complex response to external forcing. Despite observed ice front retreat and recent geophysical evidence for accelerated mass loss along Greenland's northwestern margin, it is unclear whether west Greenland glaciers have undergone the synchronous speed-up and subsequent slow-down as observed in southeastern glaciers earlier in the decade. To investigate changes in west Greenland outlet glacier dynamics and the potential controls behind their behavior, we derive time series of front position, surface elevation, and surface slope for 59 marine terminating outlet glaciers and surface speeds for select glaciers in west Greenland from 2000 to 2009. Using these data, we look for relationships between retreat, thinning, acceleration, and geometric parameters to determine the first-order controls on glacier behavior. Our data indicate that changes in front positions and surface elevations were asynchronous on annual time scales, though nearly all glaciers retreated and thinned over the decade. We found no direct relationship between retreat, acceleration, and external forcing applicable to the entire region. In regard to geometry, we found that, following retreat, (1) glaciers with grounded termini experienced more pronounced changes in dynamics than those with floating termini and (2) thinning rates declined more quickly for glaciers with steeper slopes. Overall, glacier geometry should influence outlet glacier dynamics via stress redistribution following perturbations at the front, but our data indicate that the relative importance of geometry as a control of glacier behavior is highly variable throughout west Greenland.
Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakob... more Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakobshavn Isbræ, accounted for a substantial portion of the ice sheet's mass loss over the past decade. Rapid changes in their discharge, however, make their cumulative mass-change uncertain. We derive monthly mass balance rates and cumulative balance from discharge and surface mass balance (SMB) rates for these glaciers from 2000 through 2010. Despite the dramatic changes observed at Helheim, the glacier gained mass over the period, due primarily to the short duration of acceleration and a likely longer-term positive balance. In contrast, Jakobshavn Isbræ lost an equivalent of over 11 times the average annual SMB and loss continues to accelerate. Kangerdlugssuaq lost over 7 times its annual average SMB, but loss has returned to the 2000 rate. These differences point to contrasts in the long-term evolution of these glaciers and the danger in basing predictions on extrapolations of recent changes.
This article evaluates UAV photogrammetry systems using smartphones and smart cameras. Image tria... more This article evaluates UAV photogrammetry systems using smartphones and smart cameras. Image triangulation was conducted in accordance with interior orientation parameters, determined by camera self-calibration. Precise orthomosaic images and digital surface models were generated, and their accuracy was assessed using aerial and terrestrial lidar data. Digital surface models were used to estimate earthwork volumes and verify the suitability of UAV photogrammetry for use on construction sites. Georeferencing accuracy shows that the smart camera performs about twice as well as the smartphone with reference to checkpoints and polygon parts. Considering rolling shutter in the smartphone, it is possible to increase accuracy. Especially in inclined and rugged topography, the smartphone can benefit from applying the rolling-shutter method. Earthwork of volume error is often applied as a legal requirement for some countries, and our findings indicate that a smart camera with a drone can be ...
Geografiska Annaler: Series A, Physical Geography, 2017
ABSTRACT To estimate hydrological storage and better understand the climatic implications of glac... more ABSTRACT To estimate hydrological storage and better understand the climatic implications of glacier retreat, the volume of glacial ice is a critical but problematic variable. High-accuracy mapping of glacier surface changes over time can directly estimate volume changes, allowing for explicit testing and refining of scaling relationships between changes in glacier volume and surface area that are necessary for making an inventory of remaining glacier mass with remote imagery. A combination of airborne LiDAR, spaceborne remote sensing imagery, digital photogrammetry, and geospatial techniques is used to assess the changes in volume and surface area of six glaciers in the Cordillera Blanca, Peru, between 1962 and 2008. The loss of glacier surface area ranges from 30.79% to 72.62%, corresponding to individual glacier volume changes ranging from 0.019 to 0.150 km3. The volume–surface area scaling is deduced from the change in volume related to the change in surface area by a power relationship quantified from 13 different epoch series. The result shows that there is about 36% more volume loss relative to the loss expected from surface area alone of these individual glaciers in the study area than other glaciers in mid- and high-latitudes from the previous study. Since the error of volume estimation shows a much larger impact on the increase with the size of glaciers, volume–surface area scaling analysis needs to include larger ice masses with regional inventories for a more accurate estimation.
Evaluating the historical contribution of the volume loss of ice to stream flow based on reconstr... more Evaluating the historical contribution of the volume loss of ice to stream flow based on reconstructed volume changes through the Little Ice Age (LIA) can be directly related to the understanding of glacier-hydrology in the current epoch of rapid glacier loss that has disquieting implications for a water resource in the Cordillera Blanca in the Peruvian Andes. However, the accurate prediction of the future glacial meltwater availability for the developing regional Andean society needs more extensive quantitative estimation from long-term glacial meltwater of reconstructed glacial volume. Modeling the LIA paleoglaciers through the mid-19th century (with the most extensive recent period of mountain glacier expansion having occurred around 1850 AD) in different catchments of the Cordillera Blanca allows us to reconstruct glacier volume and its change from likely combinations of climatic control variables and time. We computed the rate and magnitude of centennial-scale glacier volume ch...
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Papers by Yushin Ahn