The FORUM End-to-End Simulator project: architecture and results

Abstract

Abstract. FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will flight as the 9th ESA’s Earth Explorer mission, and an End-to-End Simulator (E2ES) has been developed as a support tool for the mission selection process and the subsequent development phases. The current status of the FORUM E2ES project is presented, together with the characterization of the capabilities of a full physics retrieval code applied to FORUM data. We show how the instrument characteristics and5the observed scene conditions impact on the spectrum measured by the instrument, accounting for the main sources of error related to the entire acquisition process, and the consequences on the retrieval algorithm. Both homogeneous and heterogeneous case studies are simulated in clear and cloudy conditions, validating the E2ES against two independent codes: KLIMA (clear sky) and SACR (cloudy sky). The performed tests show that the performance of the retrieval algorithm is compliant with the project requirements both in clear and cloudy conditions. The far infrared (FIR) part of the FORUM spectrum is shown to be10sensitive to surface emissivity, in dry atmospheric conditions, and to cirrus clouds, resulting in improved performance of the retrieval algorithm in these conditions. The retrieval errors increase with increasing the scene heterogeneity, both in terms of surface characteristics and in terms of fractional cloud cover of the scene.

Retrieval of Tropospheric Water Vapor From Airborne Far‐Infrared Measurements: A Case Study

“…We use the retrieval framework developed specifically for the FORUM End‐to‐End Simulator (Sgheri et al., 2021), which has, at its heart, an optimal estimation approach. The a‐priori information for the retrievals are the closest temperature and humidity profiles in space and time taken from the UM global forecast model.…”

“…The retrievals were performed using the L2M_I (Level 2 Module – Inversion) code, which was written for the FORUM End‐to‐End simulator ESA project (Sgheri et al., 2021). This is a standalone software for the solution of the inverse radiative transfer problem in clear or cloudy sky conditions and can perform estimates of selected geophysical parameters including surface temperature and emissivity, and vertical profiles of atmospheric temperature and volume mixing ratios of several gaseous species.…”

The Far-Infrared Radiation Mobile Observation System for spectral characterisation of the atmospheric emission

“…forward and retrieval models (Sgheri et al, 2021;Ridolfi et al, 2020;Del Bianco et al, 2013;Bianchini et al, 2008;Carli et al, 2007) to derive geophysical products (L2). Only spectra acquired from the instrument channel one were used since the second 245 channel occasionally showed a degradation that could have a negative impact on the results.…”

Synergistic Use of Far‐ and Mid‐Infrared Spectral Radiances for Satellite‐Based Detection of Polar Ice Clouds Over Ocean

“…Recent studies have investigated the use of high spectral resolution far‐IR radiances for cloud phase classification (i.e., Cossich et al., 2021; Maestri, Arosio, et al., 2019; Maestri, Cossich, & Sbrolli, 2019; Sgheri et al., 2021) based on observed downwelling radiances and synthetic satellite observations. These studies utilize numerous spectral channels across the far‐IR and mid‐IR for the radiance inputs to a principal component analysis‐based machine learning algorithm for cloud identification.…”