Using Sounder Data to Improve Cirrus Cloud Height Estimation from Satellite Imagers

Abstract

<jats:title>Abstract</jats:title> <jats:p>Modern polar-orbiting meteorological satellites provide both imaging and sounding observations simultaneously. Most imagers, however, do not have H2O and CO2 absorption bands and therefore struggle to accurately estimate the height of optically thin cirrus clouds. Sounders provide these needed observations, but at a spatial resolution that is too coarse to resolve many important cloud structures. This paper presents a technique to merge sounder and imager observations with the goal of maintaining the details offered by the imager’s high spatial resolution and the accuracy offered by the sounder’s spectral information. The technique involves deriving cloud temperatures from the sounder observations, interpolating the sounder temperatures to the imager pixels, and using the sounder temperatures as an additional constraint in the imager cloud height optimal estimation approach. This technique is demonstrated using collocated VIIRS and Cross-track Infrared Sounder (CrIS) observations with the impact of the sounder observations validated using coincident CALIPSO/CALIOP cloud heights These comparisons show significant improvement in the cloud heights for optically thin cirrus. The technique should be generally applicable to other imager/sounder pairs.</jats:p>

Improvement in cloud retrievals from VIIRS through the use of infrared absorption channels constructed from VIIRS-CrIS data fusion

“…The optimal use of the fusion channels deserves further study. 15 While both Heidinger et al (2019) and this study address the same problem with different approaches involving similar channels from the CrIS sounder, both studies show positive impact when using the sounder channels. However, Heidinger et al (2019) showed that the major improvement of ice cloud height retrieval was for those in emissivity ranges 0 to 0.4.…”

“…15 While both Heidinger et al (2019) and this study address the same problem with different approaches involving similar channels from the CrIS sounder, both studies show positive impact when using the sounder channels. However, Heidinger et al (2019) showed that the major improvement of ice cloud height retrieval was for those in emissivity ranges 0 to 0.4. This study 10 suggests that using the fusion channels may have a greater impact on the ice clouds with emissivity ranges between 0.4 and 0.8. https://doi.org/10.5194/amt-2019-497 Preprint.…”

“…April and October 2018 and one week of NOAA-20 data from January 2019. Collocations with CALIPSO are selected as described in Heidinger et al (2019). Briefly summarized, the time difference must be within 15 minutes between VIIRS and CALIPSO and the spatial distance must be within 4°.…”

“…While both Version 3 and 4 CALIPSO/CALIOP products are available, the latest Version 4-20 cloud layer product is 5 used (Vaughan et al, 2018;Avery et al, 2019). In this paper, the true CALIPSO/CALIOP cloud top height for the uppermost cloud layer is used for validation instead of an adjusted CALIPSO/CALIOP cloud top height as described in Heidinger et al (2019).…”

“…Previous studies retrieved cloud top height directly from sounder data (Susskind et al 2003;Li et al 2005;Kahn et al 2007) but the spatial resolution of the sounder is much lower than that of the companion imager. Heidinger et al (2019) developed a method to match sounder fields-of-view (FOVs; 15-km spatial resolution at nadir) and VIIRS imager pixels (750m at nadir), and adopted the ice cloud top height retrieval from the sounder as the a-priori value to improve the imager-5 based cloud height retrieval using an optimal estimation approach. Here we denote field-of-view for the sounder and pixel for the imager exclusively to minimize confusion between the two sensors.…”