Monitoring the Tropospheric Monitoring Instrument (TROPOMI) short-wave infrared (SWIR) module instrument stability using desert sites

Abstract

Abstract. Since its launch in 2017, Tropospheric Monitoring Instrument (TROPOMI) on S-5P has provided very high quality data using daily global coverage for a number of key atmospheric trace gases. Over its first 1000 d in operation, the short-wave infrared (SWIR) module has been very stable, and the continuously monitored calibration has remained of high quality. This calibration relies on a combination of extensive pre-launch and post-launch measurements, complemented by regular monitoring of internal light sources and background measurements. In this paper we present a method and results for independent validation of the SWIR module calibration and instrument stability by examining the signal stability of a sample of 23 pseudo-invariant calibration desert sites. The data covers over 2 years of operational data. With a Lambertian surface assumption, the results show that the SWIR module has little to no instrument degradation down to an accuracy of about 0.3 % yr−1, validating results obtained from the internal calibration suite. The method presented here will be used as ongoing validation of the SWIR calibration.

Vicarious calibration of the Tropospheric Monitoring Instrument (TROPOMI) short-wave infrared (SWIR) module over the Railroad Valley Playa

“…to the calibration in comparison to the on-ground results (van Kempen et al, 2019;Ludewig et al, 2020). Instrument monitoring is available online 5 and affirms the continuing excellent performance of the TROPOMI-SWIR module up to the current date of writing.…”

“…every three-five orbits). This is used not just for the retrieval of the TROPOMI products but also for calibration purposes (Kleipool et al, 2018;van Kempen et al, 2019;Ludewig et al, 2020).…”

“…The instrument calibration of TROPOMI, derived from pre-flight, on-ground measurements, commissioning data, and monitoring data, is described in a set of papers led by the Expert Support Laboratory for the Level-1 processor of the TROPOMI Mission Performance Center Tol et al, 2018;Kleipool et al, 2018;van Kempen et al, 2019;Ludewig et al, 2020). The current instrument stability of the SWIR module, for which independent validation was done in van Kempen et al (2021), can be found in the SRON online monitoring system. 7…”

“…S5p is part of the Copernicus programme headed by the European Commission in partnership with the European Space Agency (ESA). TROPOMI is the first Copernicus instrument aimed at monitoring the chemical composition of Earth's atmosphere over time (for an overview of the instrument design and performance, including the immersed grating, see, for example, Veefkind et al, 2012;Hoogeveen et al, 2013;van Amerongen et al, 2017;Kleipool et al, 2018;van Kempen et al, 2019;and Ludewig et al, 2020) The instrument consists of two modules: the UVN module, covering ultraviolet (UV), visible (VIS), and near-infrared (NIR) wavelengths, and the short-wave infrared (SWIR) module, 2 which contains an immersed grating 3 (van Amerongen et al, 2017) and a HgCdTe detector 4 measuring the short-wave infrared wavelengths between 2305 and 2385 nm. The SWIR module was specifically designed to measure the dry air columns of carbon monoxide (CO) and methane (CH 4 ).…”

“…the relative radiometric calibration) but provides relatively poor results regarding absolute radiometry. For TROPOMI-SWIR this was done using desert sites in the Sahara, Saudi Arabia, and Namibia (van Kempen et al, 2021). The other two methods rely on external measurements, from either complementary space-based sensors (i.e.…”