Optical Ground Support Equipment Research Articles

Calibration OGSEs for multichannel radiometers for Mars atmosphere studies

This work describes several Optical Ground Support Equipment (OGSEs) developed by INTA (Spanish Institute of Aerospace Technology—Instituto Nacional de Tecnica Aeroespacial) for the calibration and characterization of their self-manufactured multichannel radiometers (solar irradiance sensors—SIS) developed for working on the surface of Mars and studying the atmosphere of that planet. Nowadays, INTA is developing two SIS for the ESA ExoMars 2020 and for the JPL/NASA Mars 2020 missions. These calibration OGSEs have been improved since the first model in 2011 developed for Mars MetNet Precursor mission. This work describes the currently used OGSE. Calibration tests provide an objective evidence of the SIS performance, allowing the conversion of the electrical sensor output into accurate physical measurements (irradiance) with uncertainty bounds. Calibration results of the SIS on board of the Dust characterisation, Risk assessment, and Environment Analyzer on the Martian Surface (DREAMS) on board the ExoMars 2016 Schiaparelli module (EDM—entry and descent module) are also presented, as well as their error propagation. Theoretical precision and accuracy of the instrument are determined by these results. Two types of OGSE are used as a function of the pursued aim: calibration OGSEs and Optical Fast Verification (OFV) GSE. Calibration OGSEs consist of three setups which characterize with the highest possible accuracy, the responsivity, the angular response and the thermal behavior; OFV OGSE verify that the performance of the sensor is close to nominal after every environmental and qualification test. Results show that the accuracy of the calibrated sensors is a function of the accuracy of the optical detectors and of the light conditions. For normal direct incidence and diffuse light, the accuracy is in the same order of uncertainty as that of the reference cell used for fixing the irradiance, which is about 1%.

MTF DETERMINATION OF SENTINEL-4 DETECTOR ARRAYS

Abstract. The Institute for Optical Sensor Systems was involved in many international space projects in recent years. These include, for example, the fokal plane array (FPA) of the hyperspectral sensors ENMAP or Sentinel-4, but also the FPA for the high resolution FPA for Kompsat-3. An important requirement of the customer is the measurement of the detector MTF for different wavelengths. A measuring station under clean room conditions and evaluation algorithms was developed for these measurements. The measurement setup consist of a collimator with slit target in focus for illumination at infinity, a gimbal mounted detector facing an auxiliary lens in front, a halogen lamp with monochromator or filter, as well as optical and electrical ground support equipment. Different targets and therefore also different measurement and data evaluation opportunities are possible with this setup. Examples are slit, edge, pin hole but also a Siemens star. The article describes the measurement setup, the different measuring and evaluation procedures and exemplary results for Sentinel-4 detector.