Measuring Stratospheric H2O With an Airborne Spectrometer: Simulation With Realistic Detector Characteristics

This study examines the ability of a realistic spectral sensor flying at the tropopause level for retrieving stratospheric H₂O and temperature. This paper is an extension of an earlier study; the assumptions to best fit the characteristics of the operational sensors have been updated with the noise characteristics of real sensors. Several tests are conducted to examine the effects of changing spectral coverage and noise level on the quality of the retrieval. The results show that the potential advantage of including far infrared (IR) in the sensor´s spectral coverage is hindered by the realistic noise level of the sensors under consideration. Under the current technology, enabling the far IR at the cost of mid-IR accuracy does not help improve H₂O retrieval. Nevertheless, it is possible to achieve the retrieval accuracy of 0.5 ppmv for H₂O and 1 K for temperature up to 50 hPa using a realistic sensor. The high sensitivity retrieval is advantageous for detecting the small temporal/spatial scale lower stratospheric moistening episodes.