Across-track Extension of Retrieved Cloud and Aerosol Properties for the EarthCARE Mission: The ACM-3D Product

Abstract

Abstract. The narrow cross-section of cloud and aerosol properties retrieved by L2-algorithms that operate on data from EarthCARE’s nadir-pointing sensors gets “broadened” across-track by an algorithm that is described and demonstrated here. This Scene Construction Algorithm (SCA) consists of four sub-algorithms. At its core is a radiance-matching procedure that works with measurements made by EarthCARE’s Multi-Spectral Imager (MSI). In essence, an off-nadir pixel gets filled with retrieved profiles that are associated with a (nearby) nadir pixel whose MSI radiances best match those of the off-nadir pixel. The SCA constructs a 3D array of cloud and aerosol (and surface) properties for entire frames that measure ~6,000 km along-track by 150 km across-track (i.e., the MSI’s full swath). Constructed domains out to ~15 km on both sides of nadir are used explicitly downstream as input for 3D radiative transfer models that predict top-of-atmosphere (TOA) broadband solar and thermal fluxes and radiances. These quantities are compared to com-mensurate measurements made by EarthCARE’s BroadBand Radiometer (BBR), thus facilitating a continuous closure assessment of the retrievals. Three 6,000 km x 200 km frames of synthetic EarthCARE observations were used to demonstrate the SCA. The main conclusion is that errors in modelled TOA fluxes that stem from use of 3D domains produced by the SCA are expected to be less than ±5 W m-2 and rarely larger than ±10 W m-2. As such, the SCA, as purveyor of in-formation needed to run 3D radiative transfer models, should help more than hinder the radiative closure assessment of EarthCARE’s L2 retrievals.

The EarthCARE Mission – Science and System Overview

“…The MSI nadir pixel is used in the retrieval of synergistic products with ATLID (Haarig et al, 2022) or ATLID and CPR . Across-track data of selected MSI channels are furthermore used for the creation of 3D scenes (Qu et al, 2022a), which are needed for 1D and 3D radiative transfer calculations to calculate radiative properties Oikawa et al, 2018;Okata et al, 2017;Yamauchi et al, 2022) and perform closure assessment . The MSI is also used to improve the unfiltering of BBR measured radiances .…”

“…However, the instrument's concept of high-resolution sampling of total wave and short wave allows for flexibility in the integrated scene size. It is useful for some applications to integrate scenes of approximately the same area of 100 km 2 -in order to maintain the signal-to-noise performance -but in a narrower strip around the nadir with accordingly longer along-track dimension, as it is done by Qu et al (2022a), who is constructing 5 km × 21 km scenes for radiative transfer applications. (Note, 21 km scene length is used for this application, rather than 20 km, because of the 7-km along-track periods of the joint retrieval grid, defined in the Level 1d data product X-JSG (Eisinger et al, 2022).…”

Cloud top heights and aerosol columnar properties from combined EarthCARE lidar and imager observations: the AM-CTH and AM-ACD products

“…It is an unprecedented observational setup which will offer novel opportunities in atmospheric research beyond the initial mission goals. CPR, ATLID and MSI are used to retrieve a three-dimensional (3D) scene (e.g., Qu et al, 2022a;Mason et al, 2022) to calculate the radiative flux which is compared to the radiometer (BBR) measurements on board (Barker et al, 2023). The European and Canadian EarthCARE processing chain is presented by Eisinger et al (2023).…”

“…AM-COL extends the ATLID information over the entire swath as long as a swath pixel can be related to a track pixel. A more sophisticated approach including raditative transfer simulations is used for the pixels close to the track in the ACM-3D product (Qu et al, 2022a). They prepare the data for the 100 km 2 snapshot (20 km along track × 5 km across track) which will be used for the radiative closure.…”

Cloud top heights and aerosol layer properties from EarthCARE lidar observations: the A-CTH and A-ALD products

“…The passive imager MSI provides observations of columnar aerosol and cloud properties across a 150 km wide swath (Docter et al, 2023;Hünerbein et al, 2022Hünerbein et al, , 2023, which are used to extend the 2D cross sections from lidar and radar into the 3D domain (Haarig et al, 2023;Qu et al, 2022a). With this approach, 3D radiation modeling and closure assessments become possible, i.e., modeled TOA radiances and fluxes can be compared with those derived from BBR measurements (Cole et al, 2022;Barker et al, 2022).…”