Michel Viollier

The ScaRaB project: earth radiation budget observations from the meteor satellites

France, Russia, and Germany are cooperating in the construction and calibration of a Scanning Radiometer for Radiation Balance (ScaRaB), to be flown on the Soviet/Russian Meteor-3 series polar orbiting weather satellites, with launches scheduled annually beginning in summer 1993. The instrument comprises 2 broad channels (total, solar) for radiation budget, and 2 narrower bands for scene identification, with spatial resolution 60 km at nadir. We describe the instrument design and calibration procedures. The data processing algorithms follow the general lines adopted in the NASA Earth Radiation Budget Experiment (ERBE) so as to ensure continuity in the long-term series of data. We describe the data products which will be archived and made available to the international scientific community.

Review of capabilities of multi-angle and polarization cloud measurements from POLDER

Abstract Polarization and directionality of the Earth’s reflectances (POLDER) is a multispectral imaging radiometer–polarimeter with a wide field-of-view, a moderate spatial resolution, and a multi-angle viewing capability. It functioned nominally aboard ADEOS1 from November 1996 to June 1997. When the satellite passes over a target, POLDER allows to observe it under up to 14 different viewing directions and in several narrow spectral bands of the visible and near-infrared spectrum (443–910 nm). This new type of multi-angle instruments offers new opportunity for deriving cloud parameters at global scale. The aim of this short overview paper is to point out the main contributions of such an instrument for cloud study through its original instrumental capabilities (multidirectionality, multipolarization, and multispectrality). This is mainly illustrated by using ADEOS 1-POLDER derived cloud parameters which are operationally processed by CNES and are available since the beginning of 1999.

Inter‐calibration of CERES and ScaRaB Earth Radiation Budget datasets using temporally and spatially collocated radiance measurements

Comparisons of radiance measurements from overlapping independent Earth and cloud radiation budget (ERB) missions are an important contribution to the validation process of these missions and are essential to the construction of a consistent long-term record of ERB observations. Measurements from two scanning radiometers of different design and calibration, the Clouds and the Earths Radiant Energy System (CERES) and the Scanner for Radiation Budget (ScaRaB), are compared during simultaneous operation in January and March 1999. The instruments are found to be consistent to within 0.5% and 1.5% in the longwave and shortwave spectral domains, respectively.

Top-of-Atmosphere Radiance-to-Flux Conversion in the SW Domain for the ScaRaB-3 Instrument on Megha-Tropiques

Abstract The earth radiation budget (ERB) is the difference between the solar absorbed flux and the terrestrial emitted flux. These fluxes are calculated from satellite measurements of outgoing shortwave (SW) and longwave (LW) radiances using empirical or theoretical models of the radiation anisotropy, which are called angular distribution models (ADMs). Owing to multidirectional measurement analyses and synergy with multispectral information at subpixel scale, the ADM developed for the NASA Clouds and the Earth’s Radiant Energy System (CERES) mission is presently the best knowledge and has to be taken into account for future ERB missions, such as the Indian–French Megha-Tropiques mission to be launched in 2010. This mission will carry an ERB instrument called the Scanner for Radiation Budget (ScaRaB). To prepare the algorithms for the ScaRaB ADM retrievals, the artificial neural network (ANN) method described by the CERES team has been adopted and improved by replacing the broadband (BB) radiances by nar...

Regional Diurnal Albedo Climatology and Diurnal Time Extrapolation of Reflected Solar Flux Observations: Application to the ScaRaB Record

Abstract A regional (2.5° × 2.5° resolved) diurnal (hourly) albedo climatology for low and midlatitudes is derived for each month from the 5⅓-yr narrow-field-of-view data record obtained from the Earth Radiation Budget Satellite (ERBS). It is used in a quasi-operational diurnal interpolation/extrapolation procedure (DIEP) to calculate regional monthly means of the reflected shortwave radiation flux (RSR) from instantaneous albedo observations. This climatological approach (CDIEP) replaces the questionable assumption of diurnally constant cloud conditions made in the conventional DIEP by assuming a diurnal variation of cloudiness corresponding to the mean long-term diurnal variation of the planetary albedo. Validation of CDIEP, using the three-satellite Earth Radiation Budget Experiment (ERBE) data for December of 1986, indicates that on regional scales monthly time sampling errors for single satellite products are generally reduced but not completely removed in comparison with the currently applied diurna...

Determination of Shortwave Earth Reflectances from Visible Radiance Measurements: Error Estimate Using ScaRaB Data

Abstract The error resulting from the use of a visible channel to estimate shortwave (SW) (0.2–4 μm) fluxes reflected by the earth is analyzed. First, the authors compute regression coefficients between visible (0.55–0.65 μm) and SW radiance measurements made by the ScaRaB (Scanner for Radiation Budget) instrument aboard the Meteor-3/7 satellite between March 1994 and February 1995. These regression coefficients are computed from the 10 months of available ScaRaB measurements in different classes of geotypes and different classes of solar and viewing angles. The regression is applied to the visible radiance measurements to simulate the SW measurements in the operational processing of ScaRaB. For instantaneous fluxes, the visible-to-SW conversion gives a standard deviation of the error smaller than 8%. By comparison, the standard deviation of the instantaneous flux error coming from the angular sampling and the bidirectional reflectance uncertainty is estimated to be about 10%. For monthly mean values the ...

Radiometric and Spectral Characteristics of the ScaRaB-3 Instrument on Megha-Tropiques: Comparisons with ERBE, CERES, and GERB

Abstract The Indian–French Megha-Tropiques mission, scheduled to be launched in 2010, will carry radiation and microwave sensors to study the energy and water cycle in the tropics. The radiation sensor, the third model of the Scanner for Radiation Budget (ScaRaB-3), is dedicated to the earth’s radiation budget, the difference between the solar absorbed flux and the terrestrial emitted flux. These fluxes are calculated from satellite measurements of outgoing shortwave (SW) and longwave (LW) radiances using angular distribution models (ADMs). For practical reasons, the LW radiation is calculated from the difference between a total (T) channel (0.2–100 μm) and an SW channel (0.2–4 μm). With the ADM application, the radiance calibration remains the most critical issue in the radiation budget estimation. The 1% accuracy goal is difficult to achieve, specifically in the SW domain. The authors explain their efforts to improve the radiometric calibration of ScaRaB-3. The internal calibration module is improved: t...

True Along-Track Scan to Improve Radiation Budget Estimations

Abstract Multiangle approaches for radiance-to-flux conversion require accurate coregistration between the observations from nadir- and oblique-viewing directions. The along-track mode of Earth Radiation Budget (ERB) scanning instruments, such as the Clouds and the Earth’s Radiant Energy System (CERES), provides some multiangular observations with almost the same target observed from nadir, aft, and fore directions. To improve the overlaps of multiangle observations, this study explains how to introduce a yaw steering angle in the along-track scan mode so as to reduce the residual collocations errors. The implementation of this correction to the CERES/Terra along-track mode shows that the distances between the nadir and the oblique (55°) observations are reduced from about 40 to 2 km. Both oblique radiances are shown to be equal with small rms differences: 3.9% (all scenes) and 1.8% (homogeneous scenes), compared, respectively, to 7.0% and 3.5% before the scan adjustment.