Abstract
Abstract. Wide-field spectrometers for Earth observation missions require in-flight radiometric calibration for which the Sun can be used as a known reference. Therefore, a diffuser is placed in front of the spectrometer in order to scatter the incoming light into the entrance slit and provide homogeneous illumination. The diffuser, however, introduces interference patterns known as speckles into the system, yielding potentially significant intensity variations at the detector plane, called spectral features. There have been several approaches implemented to characterize the spectral features of a spectrometer, e.g., end-to-end measurements with representative instruments. Additionally, in previous publications a measurement technique was proposed, which is based on the acquisition of monochromatic speckles in the entrance slit following a numerical propagation through the disperser to the detection plane. Based on this measurement technique, we present a stand-alone prediction model for the magnitude of spectral features in imaging spectrometers, requiring only few input parameters and, therefore, mitigating the need for expensive measurement campaigns.
Highlights
Many current and future Earth observation missions carry wide-field spectrometer payloads, such as the Envisat Medium Resolution Imaging Spectrometer (Olij et al, 1997), the Sentinel-2 Multispectral Imager (Martimort et al, 2012), the Sentinel-3a Ocean and Land Colour Imager (Nieke and Mavrocordatos, 2017), the Sentinel-4/UVN instrument (Clermont et al, 2019), the Sentinel-5/UVNS instrument (Guehne et al, 2017), and the Greenhouse Gas Information System (GHGIS) instrument of CO2M or the former CarbonSat (Fletcher et al, 2015)
Wide-field spectrometers for Earth observation missions require in-flight radiometric calibration for which the Sun can be used as a known reference
The speckles propagate through the disperser and are integrated at the detector plane, yielding intensity variations described as spectral features by van Brug et al (2004)
Summary
Many current and future Earth observation missions carry wide-field spectrometer payloads, such as the Envisat Medium Resolution Imaging Spectrometer (Olij et al, 1997), the Sentinel-2 Multispectral Imager (Martimort et al, 2012), the Sentinel-3a Ocean and Land Colour Imager (Nieke and Mavrocordatos, 2017), the Sentinel-4/UVN instrument (Clermont et al, 2019), the Sentinel-5/UVNS instrument (Guehne et al, 2017), and the Greenhouse Gas Information System (GHGIS) instrument of CO2M or the former CarbonSat (Fletcher et al, 2015). Some simplifying assumptions are made about the optical system, which reduces the complexity and limits systematic error contributions It is only limited by the signal-to-noise ratio (SNR) and the resolution achieved in the entrance slit and is, capable of yielding comprehensive measurement data for most instrument designs. It allows for a stepby-step tracing of the speckle statistics from the slit to the detector plane Based on this SFA measurement technique, we present a novel, stand-alone SFA prediction model, which solely relies on mathematical descriptions of the speckle statistic and its SFA impact. It includes the polarization effects of the diffuser, spatial and spectral averaging, and pixel averaging at the detector. We discuss the applicability to a real instrument
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