Abstract
Abstract. Cirrus plays an important role in atmospheric radiation. It affects weather system and climate change. Satellite remote sensing is an important kind of observation for cloud. As a passive remote sensing instrument, large bias was found for thin cirrus cloud top height retrieval from MODIS (Moderate Resolution Imaging Spectroradiometer). Comparatively, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) aboard CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) which is an active remote sensing instrument can acquire more accurate characteristics of thin cirrus cloud. In this study, CALIPSO cirrus cloud top height data was used to correct MODIS cirrus cloud top height. The data analysis area was selected in Beijing-Tianjin-Hebei region and data came from 2013 to 2017. Linear fitting method was selected based on cross-validation method between MODIS and CALIPSO data. The results shows that the difference between MODIS and CALIPSO changes from −3~2 km to −2.0~2.5 km, and the maximum difference changes from about −0.8 km to about 0.2 km. In the context of different vertical levels and cloud optical depth, MODIS cirrus cloud top height is improved after correcting, which is more obvious at lower cloud top height and optical thinner cirrus.
Highlights
Cirrus is a kind of high-level cloud which is located in the middle to upper troposphere and the lower stratosphere
Because CALIPSO-CALIOP is more sensitive to thin cloud and more accurate in estimating the height of cirrus cloud top (Weisz et al, 2007), it is usually used as a kind of validation data for passive remote sensing products
After correction (Figure 3b), the peak height of MODIS cloud top is around 11 km, which is closer to the probability distribution curve of CALIPSO
Summary
Cirrus is a kind of high-level cloud which is located in the middle to upper troposphere and the lower stratosphere. As active remote sensing detectors, CPR (Cloud Profile Radar) onboard CloudSat and CALIOP (CloudAerosol Lidar with Orthogonal Polarization) onboard CALIPSO have great abilities of vertical detection (Stephens et al, 2002; Wang and Sassen, 2002). They can emit radiation which can penetrate into the interior of clouds and obtain vertical structure information, e.g., cloud top and cloud bottom height (Nazaryan et al, 2008; Haladay et al, 2009; Heidinger et al, 2010; Thorsen et al, 2011; Zhang et al, 2015; Yang et al, 2014, 2017, 2018). Because CALIPSO-CALIOP is more sensitive to thin cloud and more accurate in estimating the height of cirrus cloud top (Weisz et al, 2007), it is usually used as a kind of validation data for passive remote sensing products. Holz et al (2008) pointed out that MODIS underestimated the cloud top height of thin optical clouds when the cloud top height was greater than 5 km, based on CALIOP. Menzel et al (2013) used CALIOP data to evaluate MODIS MOD06 products and found a significant negative bias of cloud top height between MOD06 and CALIOP, especially for cirrus
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