PARASOL in-flight calibration and performance

Abstract

Since 18 December 2004, the PARASOL satellite is a member of the so-called A-train atmospheric orbital observatory, flying together with Aqua, Aura, CALIPSO, CLOUDSAT, and OCO satellites. These satellites combine for the first time a full suite of instruments for observing aerosols and clouds, using passive radiometer complementarily with active lidar and radar sounders. The PARASOL payload is extensively derived from the instrument developed for the POLDER programs that performs measurements of bidirectionality and polarization for a very wide field-of-view and for a visible͞near-infrared spectral range. An overview of the results obtained during the commissioning phase and the reevaluation after one year in orbit is presented. In-flight calibration methods are briefly described, and radiometric and geometric performances are both evaluated. All algorithms are based on a panel of methods using mainly natural targets previously developed for POLDER missions and adapted or redeveloped in the PARASOL context. Regarding performances, all mission requirements are met except for band 443 (not recommended for use). After one year in orbit, a perfect geometrical stability was found while a slight decrease of the radiometric sensitivity was observed and corrected through an innovative multitemporal algorithm based on observations of bright and scattered convective clouds. The scientific exploitation of PARASOL has now begun, particularly by coupling these specific observations with other A-train sensor measurements.

Impact of cloud horizontal inhomogeneity and directional sampling on the retrieval of cloud droplet size by the POLDER instrument

“…For noise contributions larger than the 10 % of the signal, the RMSE values of the CDR estimate increase rapidly. The instrument-and calibrationrelated noise in the POLDER-measured polarized reflectance values is considered to be within 3 % (van Diedenhoven et al, 2012;Fougnie et al, 2007). These results confirm that the inversion is robust as long as the noise contributions do not exceed 10 % of the valid signal, even if the observations are limited.…”

“…The CDR values of the clouds ranged from 5 to 20 µm in 1 µm increments, and the EV values were 0.01, 0.02, and 0.05. Three COT values (1, 5, and 10) were considered in this study, and the contributions from the underlying surface and the aerosol and molecule layers are negligible (Coddington et al, 2010;Goloub et al, 2000). The Rayleigh optical thickness for different wavelengths was set according to the results of Bodhaine et al (1999).…”

“…However, the POLDER observations are not always optimal, and noise may be introduced by instruments, the transmission of the signal, and/or the inhomogeneous structure of the cloud fields. This noise can be modeled as pseudo-random errors added on the multi-angle polarized reflectances (Fougnie et al, 2007;Cairns et al, 2003).…”

“…Therefore, in the retrieval, the CDR and EV are derived simultaneously by matching the satellitemeasured polarized reflectance curve to pre-computed polarized phase functions. The structures of the rainbow and supernumerary bows are dominated by the single scattering properties of the upper layer clouds; the signal tends to saturate for cloud optical thicknesses greater than 2-3 (Bréon and Goloub, 1998;Goloub et al, 2000). Surface albedo (surface type) can then be omitted in the retrieval algorithm (Bréon and Doutriaux-Boucher, 2005).…”

Pleiades Absolute Calibration : Inflight Calibration Sites and Methodology

“…For these acquisitions, the molecular scattering signal may constitute as much as 90% of the TOA signal, for spectral bands from blue to red bands (typically 443 to 670nm). This forms the basis of the calibration method using Rayleigh scattering (Fougnie, 2007).…”