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.