The main objective of this project is the validation of DAS (differential absorbtion spectroscopy) performance models and their respective error formulations in the 2.0 - 2.5 µm spectral band by implementing a ground-based experimental setup at representative wavelengths. The activity will serve to record the first observed data in this specific configuration, which will be validated by in situ measurements. The respective retrieval software has to be developed as part of this activity. The recorded raw data should be analyzed with respect to small and broadband atmospheric effects. It will provide a baseline to critically review the currently used error formulations and reduce uncertainties. The project will help to quantify the level of precision and accuracy which can be achieved with this methodology. The raw data set (and auxiliary data) will be made available to support validation activities in general.

Description:

A differential absorption experiment based on state-of-the-art detector and laser diode technology will be implemented in a way allowing one to tune basic parameters like power or beam divergence angle to mimic different realistic observational scenarios. As optimal location the Observatorio del Roque de los Muchachos (Island of La Palma) and the Observatorio del Teide (Island of Tenerife) have been identified, which offer the necessary infrastructure and a baseline distance of ~144 km at an altitude of ~3.4 km. The OGS (ESA's optical ground station) at Teide Mountain can be used as receiver unit with the possibility to mount the detector inside, using an optical bench (this setup has been used by the QIPS (Quantum Information and Quantum Physics in Space) experiment (ESTEC/Contract No.18805/04/NL/HE)). The baseline setup should consist of four laser diodes emitting signals at ~2.1 µm and ~2.3 µm allowing to probe the atmospheric content of CO2, 13CO2, H2O and C18OO. The derived concentrations should be validated against in situ measurements taken at the transmitter and receiver locations.

Expected impact:

The recorded data set will comprise a unique set of observations and will the first data set available of this specific observational setup. This activity will provide a realistic baseline for active remote sensing in the SWIR band based on the differential absorption technique. The data set gathered during this activity will help to establish a reliable performance envelope concerning the detector and laser technology used as well as the limitations inherent due to the measurement principle. The observations will allow deriving valuable information concerning effects of atmospheric turbulence as well as other factors limiting the accuracy of the chosen remote sensing approach. It will serve to validate and improve the performance models currently in use in terms of retrieval methodology and error formulations.