Directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface measured by the GOME-2 satellite instruments

Abstract

Abstract. In this paper we introduce the new concept of directionally dependent Lambertian-equivalent reflectivity (DLER) of the Earth's surface retrieved from satellite observations. This surface DLER describes Lambertian (isotropic) surface reflection which is extended with a dependence on the satellite viewing geometry. We apply this concept to data of the GOME-2 satellite instruments, to create a global database of the reflectivity of the Earth's surface, providing surface DLER for 26 wavelength bands between 328 and 772 nm as a function of the satellite viewing angle via a second-degree polynomial parameterisation. The resolution of the database grid is 0.25 by 0.25 degrees but the real, intrinsic spatial resolution varies over the grid from 1.0 by 1.0 degrees to 0.5 by 0.5 degrees down to 0.25 by 0.25 degrees by applying dynamic gridding techniques. The database is based on more than ten years (2007–2018) of GOME-2 data from the MetOp-A and MetOp-B satellites. The relation between surface DLER and surface BRDF is studied using radiative transfer simulations. For the shorter wavelengths (λ 500 nm). Based on this outcome, the GOME-2 surface DLER is compared with MODIS surface BRDF data from MODIS band 1 (centred around 645 nm), using both case studies and global comparisons. The conclusion of this validation is that the GOME-2 DLER compares well to MODIS BRDF, and that it does so much better than the non-directional LER database. The DLER approach for describing surface reflectivity is therefore an important improvement over the standard isotropic (non-directional) LER approaches used in the past. The GOME-2 surface DLER database can be used for the retrieval of atmospheric properties from GOME-2 and from previous satellite instruments like GOME and SCIAMACHY. It will also be used to support retrievals from the future Sentinel-5/UVNS satellite instrument.

Validation of the Sentinel-5 Precursor TROPOMI cloud data with Cloudnet, Aura OMI O<sub>2</sub>–O<sub>2</sub>, MODIS, and Suomi-NPP VIIRS

“…These are effects known from other sensors (e.g. Tuinder et al, 2010). sRCF and C(T)H have a similar shape for the different products, although there are offsets.…”

“…Since GOME, all UV/VIS nadir sounders with the exception of OMI have included measurements of the oxygen A-band around 760 nm, from which two independent cloud parameters can be retrieved (Schuessler et al, 2014) -in addition to cloud height, either cloud fraction (Stammes et al, 2008) or cloud optical thickness (Loyola et al, 2010). Additional parameters like the cloud fraction (when not derived from the O 2 A-band observations) can be retrieved from UV spectral measurements (van Diedenhoven et al, 2007) or from broadband polarization monitoring devices (Loyola, 1998;Lutz et al, 2016;Grzegorski et al, 2006;Sihler et al, 2020). Its spectral range being limited to 500 nm, the effective cloud fraction and effective cloud pressure for OMI are retrieved using a DOAS (differential optical absorption spectroscopy) fit of the O 2 -O 2 absorption feature around 477 nm (Acarreta et al, 2004;Veefkind et al, 2016).…”

An improved TROPOMI tropospheric NO<sub>2</sub> research product over Europe

“…In this study we use a new algorithm developed at DLR to retrieve geometry-dependent effective LER (GE_LER) in the Vis based on the fullphysics inverse learning machine (FP_ILM) technique (Loyola et al, 2020b). Compared to the typical climatological LER or the directionally dependent (DLER) data (Tilstra et al, 2021), the GE_LER data represent the actual surface conditions better such as snow/ice scenarios based on each single TROPOMI measurement with a high spatial resolution. GE_LER has been successfully applied in the retrievals of TROPOMI total ozone columns in the UV (Loyola et al, 2020b) and cloud parameters in the NIR (Loyola et al, 2020a) and is being used in the corresponding operational version 2.1 cloud products (see further down in the Introduction).…”

Global Observations of Tropospheric Bromine Monoxide (BrO) Columns From TROPOMI

“…Surface albedo is calculated from the TROPOMI directionally dependent Lambertian‐equivalent reflectivity (DLER) product (Tilstra, 2022; Tilstra et al., 2021), depending on viewing angles. The TROPOMI DLER product is based on newer observations for 2018–2021 with a higher spatial resolution of 0.125° × 0.125° and an improved treatment of cloud contaminations (Tilstra, 2022), in comparison with the OMI or GOME‐2 LER climatologies (Kleipool et al., 2008; Tilstra et al., 2017).…”

“…𝜕𝜕 parameter is the AMF derivative, and 𝐴𝐴 𝐴𝐴𝐴𝐴 𝑠𝑠 , 𝐴𝐴 𝐴𝐴𝑓𝑓 𝑐𝑐 , 𝐴𝐴 𝐴𝐴𝑃𝑃 cloud , and σ S are typical uncertainties on the surface albedo, cloud fraction, cloud top pressure, and profile shape, respectively, assessed from the literature or inferred by comparing with independent data. The typical uncertainties are 0.027 for DLER albedo(Tilstra, 2022;Tilstra et al, 2021), 0.05 for the OCRA cloud fraction, and 50 hPa for ROCINN cloud pressure(Loyola et al, 2020).…”