Stratospheric High Altitude Pseudo-Satellites and their role in advancing understanding of the Earth's thermal emission

The Earth's thermal emission to space covers the Far-to-near-infrared (100-3000) cm-1. The majority of this emission has been covered by various satellite instruments, most recently IASI-MetOp, but the far-IR component, 100-667 cm-1, which can be up to 40% of the outgoing energy, has been neglected. A recent proposal (FORUM) for a satellite mission to fill this lack of coverage has been submitted to the ESA Earth Explorer 9 call. The low polar orbit of the mission, if selected, offers unique science but additional observations from ground or high altitude platforms are still valuable. Deployment of far-IR observational capacity such as the REFIR-PAD instrument to Chile (balloon) and Antarctica (ground) has established continuous and autonomous measurements as routine. This readily lends itself to deployment on a Stratospheric High Altitude Pseudo-Satellite (SHAPS). Coupled with similar mid-IR instrumentation SHAPS offers a unique opportunity to cover the full spectral range of Earth's thermal emission from a single platform at minimal costs. Here, we propose the use of two new instruments, a FORUM-like (100-1600 cm-1) and an IASI-like (600-3000 cm-1) instrument on board the SHAPS. The altitudes and stable location of these platforms enable the continuous monitoring of water vapour and cirrus clouds and can revolutionise the measurement of FIR surface emissivity. These observations will enable more precise measurements of cirrus radiative properties. As well as offering new measurements in the FIR the thermal overlap with IASI leads directly to coincident measurement validation and improved parameterisation of cirrus within Earth system models. Additionally to IASI this proposed use of the SHAPS offers an exciting synergy with the future deployment of the IR sounder part of EUMETSAT geostationary MTG program. The SHAPS ability to mimic the view of a geostationary platform while resolving spatial structure will provide valuable validation and diagnostic information.