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Ann. Geophys., 15, 1089-1098, 1997
www.ann-geophys.net/15/1089/1997/
© European Geosciences Union 1997
Intercalibration of HRDI and WINDII wind measurements
M. D. Burrage, W. R. Skinner, and P. B. Hays
Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109, USA
Abstract. The High Resolution Doppler Imager (HRDI)
and the Wind Imaging Interferometer (WINDII) in-
struments, which are both on the Upper Atmosphere
Research Satellite, measure winds by sensing the
Doppler shift in atmospheric emission features. Because
the two observation sets are frequently nearly coincident
in space and time, each provides a very e.ective
validation test of the other. Discrepancies due to
geophysical di.erences should be much smaller than
for comparisons with other techniques (radars, rockets,
etc.), and the very large sizes of the coincident data sets
provide excellent statistics for the study. Issues that have
been examined include relative systematic o.sets and the
wind magnitudes obtained with the two systems. A
significant zero wind position di.erence of ~6 m s–1 is
identified for the zonal component, and it appears that
this arises from an absolute perturbation in WINDII
winds of –4 m s–1 and in HRDI of +2 m s–1. Altitude
o.sets appear to be relatively small, and do not exceed
1 km. In addition, no evidence is found for the existence
of a systematic wind speed bias between HRDI and
WINDII. However, considerable day-to-day variability
is found in the quality of the agreement, and RMS
di.erences are surprisingly large, typically in the range
of 20±30 m s–1.
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