Water Vapor Retrievals from Near-infrared Channels of the Advanced Medium Resolution Spectral Imager Instrument onboard the Fengyun-3D Satellite

Abstract

Water vapor plays a key role in weather, climate and environmental research on local and global scales. Knowledge about atmospheric water vapor and its spatiotemporal variability is essential for climate and weather research. Because of the advantage of a unique temporal and spatial resolution, satellite observations provide global or regional water vapor distributions. The advanced Medium Resolution Spectral Imager (MERSI) instrument—that is, MERSI-II—onboard the Fengyun-3D (FY-3D) meteorological satellite, has been one of the major satellite sensors routinely providing precipitable water vapor (PWV) products to the community using near-infrared (NIR) measurements since June 2018. In this paper, the major updates related to the production of the NIR PWV products of MERSI-II are discussed for the first time. In addition, the water vapor retrieval algorithm based on the MERSI-II NIR channels is introduced and derivations are made over clear land areas, clouds, and sun-glint areas over the ocean. Finally, the status and samples of the MERSI-II PWV products are presented. The accuracy of MERSI-II PWV products is validated using ground-based GPS measurements. The results show that the accuracies of the water vapor products based on the updated MERSI-II instrument are significantly improved compared with those of MERSI, because MERSI-II provides a better channel setting and new calibration method. The root-mean-square error and relative bias of MERSI-II PWV products are typically 1.8–5.5 mm and −3.0% to −14.3%, respectively, and thus comparable with those of other global remote sensing products of the same type.

摘要

大气水汽在区域和全球范围的天气、气候和环境研究中起着关键作用。了解大气水汽含量及其时空变化对于气候和天气研究至关重要。卫星遥感因其具有独特的时空分辨率的优势,可提供全球或区域性的水汽分布。我国风云3D(FY-3D)气象卫星上搭载的新一代的中分辨率光谱成像仪(即MERSI-II),与NASA的MODIS属于同类型传感器,具备基于近红外通道观测反演大气可降水产品(PWV)的能力。自2018年6月以来,MERSI-II可向用户业务提供全球范围的日、旬、月的大气可降水产品。本文首先重点讨论了MERSI-II大气可降水产品反演算法中涉及的主要改进和更新。继之,介绍了MERSI-II大气可降水产品的现状及产品示例。最后,基于地面的全球定位系统GPS的水汽观测数据,对MERSI-II PWV产品的精度进行了比对验证。结果表明,MERSI-II PWV产品的均方根误差和相对偏差通常分别为1.8-5.5 mm和-3.0%--14.3%,与国际上同类型遥感仪器的水汽产品精度相当。与第一代MERSI相比,其水汽产品的精度有了显著提高主要与MERSI-II优化了通道设置,采用了新的辐射定标方法等因素有关。