|Paper title||Scene Generator Module for the TRUTHS Climate Mission|
|Form of presentation||Poster|
The Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) satellite mission is a climate mission led by the UK Space Agency (UKSA) and delivered by the European Space Agency (ESA). One of the main objectives of TRUTHS is to provide in-orbit cross-calibration traceable to SI standards for Earth observation satellite missions. The possibility of in-orbit cross-calibration will enhance the performance of calibrated sensors and allow up to a tenfold improvement in data reliability compared to existing data. The ability to obtain more reliable data will lead to improved future climate models, which are crucial for decision-making and action against climate change.
In the development process of the TRUTHS mission, an End-to-End Mission simulator is used to reproduce different mission configurations and evaluate their performance. As part of this simulator, a scene generator module is required that simulates the TRUTHS Top Of Atmosphere (TOA) radiances for several different land surface types. Reflectance cubes from NASA’s airborne imaging spectroradiometer AVIRIS-NG were used as input data for six different land surface types (ocean, agriculture, forest, snow/ice, clouds and desert). First, an extrapolation of the AVIRIS-NG spectral range to the UV range was performed in dependence of the land surface type. A spatial resampling to 2000 pixel across-track and a spectral resampling to 1nm intervals was necessary to meet the requirements of TRUTHS. Further, a simulated TRUTHS sensor file was generated and used as an input to ATCOR to compute a simulated TOA radiance of TRUTHS. ATCOR is a software product that uses the MODTRAN-5 radiative transfer equation to simulate at-sensor radiances. For the latter step, different solar zenith angles were considered to provide a minimum and maximum solar zenith angle per scene. For validation purposes, a cross-comparison was performed using TOA radiances of AVIRIS-NG and the simulated TRUTHS TOA radiances. The final products are delivered in NetCDF file format and will be used as target scenes to be observed by the TRUTHS sensor and hence to test and evaluate its performance.