The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is a 21-channel limb scanning infrared radiometer,
designed to make global measurements of temperature, ozone, water vapor, eight other gases and aerosols from 8 to as
high as 80 km. with 1 km. vertical resolution. During launch on NASA’S Aura satellite a piece of interior lining
material became lodged in the foreoptics, reducing the effective aperture by 80-95%, and inserting another signal into
the system. The HIRDLS team has worked for several years to develop corrections for these effects, and recover as
many as possible of the planned capabilities. This talk describes the last and probably final set of algorithms to recover
the planned species. Early work developed corrections for channels with large radiances allowing temperature and
ozone to be retrieved. Subsequent work has concentrated on refining these to allow species such as nitric acid,
chlorofluorocarbons 11 & 12, nitrogen dioxide, N2O5, chlorine nitrate, nitrous oxide and water vapor to be recovered.
Effort has gone into studying, then parameterizing in an adaptive way, the quasi-regular way the signal from the
blockage varies with time during an orbit and during the mission. Several recent improvements are described. Results of
these corrections show improvements in the retrieved products.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on the NASA Aura satellite in July
2004. HIRDLS is a joint project between the UK and USA, and is a mid-infrared limb emission sounder designed to
measure the concentrations of trace species, cloud and aerosol, and temperature and pressure variations in the Earth's
atmosphere from the upper troposphere to the mesosphere. The instrument is intended to make measurements at both
high vertical and horizontal spatial resolutions, but validating those measurements is difficult because few other
measurements provide that vertical resolution sufficiently closely in time. However, the FORMOSAT-3/COSMIC suite
of radio occultation satellites that exploit the U.S. GPS transmitters to obtain high resolution (~1 km) temperature
profiles in the stratosphere does provide sufficient profiles nearly coincident with those from HIRDLS. Comparisons
show a good degree intercorrelation between COSMIC and HIRDLS down to about 2 km resolution, with similar
amplitudes for each, implying that HIRDLS and COSMIC are able to measure the same small scale features. The
optical blockage that occurred within HIRDLS during launch does not seem to have affected this capability.
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