Spectral analysis of the primary flight focal plane arrays for the thermal infrared sensor

Abstract

The Thermal Infrared Sensor (TIRS) on board the Landsat Data Continuity Mission (LDCM) is a two-channel, push-broom imager that will continue Landsat thermal band measurements of the Earth. The core of the instrument consists of three Quantum Well Infrared Photodetector (QWIP) arrays whose data are combined to effectively produce a linear array of 1850 pixels for each band with a spatial resolution of approximately 100 meters and a swath width of 185 kilometers. In this push-broom configuration, each pixel may have a slightly different band shape. An on-board blackbody calibrator is used to correct each pixel. However, depending on the scene being observed, striping and other artifacts may still be present in the final data product. The science-focused mission of LDCM requires that these residual effects be understood. The analysis presented here assisted in the selection of the three flight QWIP arrays. Each pixel was scrutinized in terms of its compliance with TIRS spectral requirements. This investigation utilized laboratory spectral measurements of the arrays and filters along with radiometric modeling of the TIRS instrument and environment. These models included standard radiometry equations along with complex physics-based models such as the MODerate spectral resolution TRANsmittance (MODTRAN) and Digital Imaging and Remote Sensing Image Generation (DIRSIG) tools. The laboratory measurements and physics models were used to determine the extent of striping and other spectral artifacts that might be present in the final TIRS data product. The results demonstrate that artifacts caused by the residual pixel-to-pixel spectral non-uniformity are small enough that the data can be expected to meet the TIRS radiometric and image quality requirements.