Specifying the saturation temperature for the HyspIRI 4-μm channel

The investigation of high-temperature natural phenomena, such as wildland fires and active lava flows, is a primary science objective for the proposed Hyperspectral Infrared Imager (HyspIRI) mission. Current planning for HyspIRI includes a mid-infrared (MIR) channel centered at 4 μm that will allow measurement of radiance emitted from high-temperature targets. In this paper we present the results of a study to specify the saturation temperature for the MIR channel. This study was based on reviews of the literature, together with case studies of airborne and satellite-based data acquired over high-temperature targets. The spatial resolution of MIR radiance measurements is an important consideration in the remote sensing of high-temperature phenomena, due to the presence of materials at different temperatures within the area covered by an image pixel. The HyspIRI MIR channel will provide a spatial resolution of 60 m, which is ~40 times finer (in terms of area) than the finest spatial resolution provided by heritage instruments (370 m). This fine spatial resolution will increase the probability that high-temperature targets fill an image pixel and, therefore, the HyspIRI MIR channel will require a saturation temperature 2 to 4 times higher than the saturation limits of heritage instruments. Based on our study, we recommend a saturation temperature of 1200 K (927 °C). This recommendation accounts for the high temperatures expected for natural phenomena, expected performance of the MIR channel, and overlap in sensitivity between the MIR and thermal infrared (7.5–12 μm) HyspIRI channels.