Validation of the IASI temperature and water vapor profile retrievals by correlative radiosondes
2008
The METOP-A satellite Infrared Atmospheric Sounding Interferometer (IASI) Level 2 products comprise
retrievals of vertical profiles of temperature and water vapor. The L2 data were validated through
assessment of their error covariances and biases using radiosonde data for the reference. The radiosonde
data set includes dedicated launches as well as the ones performed at regular synoptic times at Lindenberg
station (Germany). For optimal error estimate the linear statistical Validation Assessment Model (VAM)
was used. The model establishes relation between the compared satellite and reference measurements based
on their relations to the true atmospheric state. The VAM utilizes IASI averaging kernels and statistical
characteristics of the ensembles of the reference data to allow for finite vertical resolution of the retrievals
and spatial and temporal non-coincidence. For temperature retrievals expected and assessed errors are in
good agreement; error variances/rms of a single FOV retrieval are 1K between 800 - 300 mb with an
increase to ~1K in tropopause and ~2K at the surface, possibly due to wrong surface parameters and
undetected clouds/haze. Bias against radiosondes oscillates within ±0 5K . between 950 - 100 mb. As for
water vapor, its highly variable complex spatial structure does not allow assessment of retrieval errors with
the same degree of accuracy as for temperature. Error variances/rms of a single FOV relative humidity
retrieval are between 10 - 13% RH in the 800 - 300 mb range.
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