Cloud-top pressure retrieval with DSCOVR EPIC oxygen A- and B-band observations

Abstract

Abstract. An analytic transfer inverse model for Earth Polychromatic Imaging Camera (EPIC) observations is proposed to retrieve the cloud-top pressure (CTP) with the consideration of in-cloud photon penetration. In this model, an analytic equation was developed to represent the reflection at the top of the atmosphere from above cloud, in cloud, and below cloud. The coefficients of this analytic equation can be derived from a series of EPIC simulations under different atmospheric conditions using a nonlinear regression algorithm. With estimated cloud pressure thickness, the CTP can be retrieved from EPIC observation data by solving the analytic equation. To simulate the EPIC measurements, a program package using the double-k approach was developed. Compared to line-by-line calculation, this approach can calculate high-accuracy results with a 100-fold computation time reduction. During the retrieval processes, two kinds of retrieval results, i.e., baseline CTP and retrieved CTP, are provided. The baseline CTP is derived without considering in-cloud photon penetration, and the retrieved CTP is derived by solving the analytic equation, taking into consideration in-cloud and below-cloud interactions. The retrieved CTPs for the oxygen A and B bands are smaller than their related baseline CTP. At the same time, both baseline CTP and retrieved CTP at the oxygen B band are larger than those at the oxygen A band. Compared to the difference in baseline CTP between the B band and A band, the difference in retrieved CTP between these two bands is generally reduced. Out of around 10 000 cases, in retrieved CTP between the A and B bands we found an average bias of 93 mb with a standard deviation of 81 mb. The cloud layer top pressure from Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements is used for validation. Under single-layer cloud situations, the retrieved CTPs for the oxygen A band agree well with the CTPs from CALIPSO, the mean difference of which within 5 mb in the case study. Under multiple-layer cloud situations, the CTPs derived from EPIC measurements may be larger than the CTPs of high-level thin clouds due to the effect of photon penetration.

Calibration of the DSCOVR EPIC Visible and NIR Channels using Multiple LEO Radiometers

“…In addition, EPIC data have been employed to observe volcanic clouds Carn et al (2016Carn et al ( , 2018, analyze the global distribution of erythemal irradiance Herman et al (2020); Herman et al (2018a), and observe solar eclipse irradiance changes (Herman at al., 2018b). EPIC observations in the backscattering region have been used to observe and characterize the glint caused by oriented ice crystals in clouds Varnai et al (2020); , retrieve cloud properties Yang et al (2013); Yang et al (2019); Yin et al (2020), ozone Herman et al (2018a) and vegetation properties Yang et al, 2017). More EPIC-related research papers may be found here: https:// epic.gsfc.nasa.gov/science/pubs.…”

Cloud Detection Over Sunglint Regions With Observations From the Earth Polychromatic Imaging Camera

“…Oxygen absorption has been applied to remote sensing of cloud and aerosol extensively (e.g., Fischer and Grassl, 1991;Stammes et al, 2008;Wang et al, 2008;Ferlay et al, 2010;Ding et al, 2016;Richardson et al, 2020). The EPIC's two O 2 band pairs (R 764 ∕R 780 and R 688 ∕R 680 ) are used for the retrieval of CEP (Yang et al, 2013;Davis et al, 2018a;Yang et al,2019;Yin et al, 2020) and for cloud masking over snow and ice (Zhou et al, 2020). The retrieval is based on the principle that the O 2 absorption bands are sensitive to the presence of clouds, especially high and thick clouds that reduce the absorbing air mass that light travels through while the reference channel does not.…”