Powerful New Tool for
Inter-satellite Instrument Calibration
A powerful method has been developed to quantify the inter-satellite
calibration biases for radiometers on polar-orbiting satellites. Application
of the method to the instruments of all historic NOAA POES observations will
permit the construction of high quality Climate Data Records for climate
monitoring and reanalyses. The method is based on Simultaneous Nadir
Overpass (SNO) observations. A SNO occurs when the nadir points of two
polar-orbiting satellites cross each other within a few seconds. Such
crossings occur at the orbital intersections of the satellites in
Polar Regions.  At each SNO, radiometers from each pair of satellites
view the same place at the same time at nadir, thus eliminating
uncertainties associated with the atmospheric path, view geometry, and time differences.
Their measurements should be identical. By comparing the measurements of
the two satellites during SNOs, it is possible to determine the bias of
one instrument with respect to the other.
Figure (right). Intersatellite radiance biases between HIRS Channel 3
on NOAA-15 and -16 (top curve) as determined from Simultaneous Nadir
Overpass (SNO) observations. The graph also shows that seasonal
variations in the bias are highly correlated with the lapse rate
(lower curve), indicating small spectral response differences between
the two satellite instruments.
|
