Climate Data Records from Meteosat First Generation Part II: Retrieval of the In-Flight Visible Spectral Response

Ralf Quast,Ralf Giering,Frank Rüthrich,Yves Govaerts,Rob Roebeling

doi:10.3390/rs11050480

Abstract

How can the in-flight spectral response functions of a series of decades-old broad band radiometers in Space be retrieved post-flight? This question is the key to developing Climate Data Records from the Meteosat Visible and Infrared Imager on board the Meteosat First Generation (MFG) of geostationary satellites, which acquired Earth radiance images in the Visible (VIS) broad band from 1977 to 2017. This article presents a new metrologically sound method for retrieving the VIS spectral response from matchups of pseudo-invariant calibration site (PICS) pixels with datasets of simulated top-of-atmosphere spectral radiance used as reference. Calibration sites include bright desert, open ocean and deep convective cloud targets. The absolute instrument spectral response function is decomposed into generalised Bernstein basis polynomials and a degradation function that is based on plain physical considerations and able to represent typical chromatic ageing characteristics. Retrieval uncertainties are specified in terms of an error covariance matrix, which is projected from model parameter space into the spectral response function domain and range. The retrieval method considers target type-specific biases due to errors in, e.g., the selection of PICS target pixels and the spectral radiance simulation explicitly. It has been tested with artificial and well-comprehended observational data from the Spinning Enhanced Visible and Infrared Imager on-board Meteosat Second Generation and has retrieved meaningful results for all MFG satellites apart from Meteosat-1, which was not available for analysis.

Highlights

The Meteosat Visible and Infrared Imager (MVIRI) on board the Meteosat First Generation (MFG) of geostationary satellites scanned Earth radiance every 30 min in a 0.4 μm to 1.1 μm broad band, referred to as the Visible (VIS)
How can the in-flight spectral response functions of a series of decades-old broad band radiometers in Space be retrieved post-flight? This question is the key to developing Climate Data Records from the Meteosat Visible and Infrared Imager on board the Meteosat First Generation (MFG) of geostationary satellites, which acquired Earth radiance images in the Visible (VIS) broad band from 1977 to 2017
The absolute instrument spectral response function is decomposed into generalised Bernstein basis polynomials and a degradation function that is based on plain physical considerations and able to represent typical chromatic ageing characteristics

Summary

Introduction

The Meteosat Visible and Infrared Imager (MVIRI) on board the Meteosat First Generation (MFG) of geostationary satellites scanned Earth radiance every 30 min in a 0.4 μm to 1.1 μm broad band, referred to as the Visible (VIS). The prerequisite for any CDR usually is a Fundamental Climate Data Record (FCDR) of Earth radiance (or equivalent) with accurate and traceable quantification of uncertainty per datum [6]. The missing clue to create such an FCDR from MVIRI images is adequate knowledge of the in-flight VIS spectral response function of each MFG satellite, which is not available because the VIS spectral response functions were characterised inaccurately before launch [7] and degraded continuously in Space in an unknown manner [8], a problem that has been investigated [9,10,11] but not been solved. Any available prior information on forward model parameters needs to be made explicit, and measurement (and modelling) uncertainties need to be represented carefully

Methods

Results

Conclusion