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.
A piece of plastic film came loose during launch and blocked most of the optical aperture. The largest remaining
problem in correcting the measured radiances is the removal of the signals from this blockage. The present method is
briefly described, followed by an outline of a new version, called the (ST)3 method. It relies on more understanding of
the behavior of the blockage signals acquired in previous work. The method involves Scaling and Time interpolating the
signals, Shifting them to align features, and Translating them to recover the scaled value at the reference angle. The
residuals are represented by empirical orthogonal functions, coefficients of which may be Substituted from other
channels. Finally, allowance for long-term Temporal changes in the blockage signals are being developed. Results for a
day in the middle of the mission are presented, as well as their effects on water vapor retrievals.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on NASA's Aura spacecraft on 15 July 2004. When activation was completed 25 days later, it was discovered that the measured radiances were very different from those that were expected. After a long series of analyses and diagnostic tests, the cause was confirmed to be a blockage that covers much of the front aperture, preventing even one completely clear view of the atmosphere. In this paper the steps required to correct the radiances for the effects of the blockage are noted. These are calibrating the radiances, removing the effects of the blockage oscillating, and the radiance coming from the blockage, correcting for the effects of the partial aperture, and filtering the noise. The paper describes the algorithms needed, and presents the results of their application. The success of the procedures will be demonstrated by the quality of the resulting radiances and retrieved profiles of temperature and trace species. The difficulties that have been eliminated, and that still remain are noted, along with plans for further improvement. Finally, the scientific implications are briefly discussed.
The functional performance of the NASA Aura HIRDLS instrument since launch on the 15th July 2004 is presented and discussed. The HIRDLS (High Resolution Infra-red Limb Sounder) is a 21-channel infra-red radiometer, using actively cooled MCT detectors on a common focal plane. It has many features that provide considerable flexibility of the commanding, control and the format and content of the telemetry. HIRDLS also features a precision 2-axis scan mirror
and gyroscopes that are attached to the optical bench and together they provide additional data on the line of sight on small time scales. The stability of the temperature control of the focal plane and critical optical components is also presented and discussed. To-date the instrument has performed functionally without fault and in many aspects well within specifications. The only problem (and a serious one) so far encountered has been the optical blockage of the main aperture, which is discussed in other papers. Some aspects of the instrument that have been utilised to help characterise the blockage are outlined.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is scheduled for launch on the NASA AURA satellite in January 2004; it is a joint project between the UK and USA. HIRDLS is a mid-infrared limb emission sounder which will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude on a finer spatial scale than has been achieved before. This will depend upon both a high quality of instrument build, and very precise pre-launch calibration. Proto Flight Model calibration was performed in a purpose-built laboratory at Oxford University during an 13-week period in 2002. The tests were made in vacuum under cryogenic conditions close to the space environment. The measurements were divided into spectral, spatial and radiometric, with the HIRDLS pointing capability being used to control which item of test equipment was viewed. A large degree of automation was achieved, and this combined with 24-hour/7-day working enabled a large quantity of information to be obtained.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is scheduled for launch on the NASA AURA satellite in January 2004; it is a joint project between the UK and USA. HIRDLS is a mid-infrared limb emission sounder which will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude on a finer spatial scale than been achieved before. HIRDLS has particularly stringent radiometric calibration accuracy requirements. A warm (280-300K) 'In-Flight Calibrator' (IFC) black cavity within the instrument plus a view to cold space are used to perform radiometric calibration. The cavity has an entrance aperture which is much smaller than the full beam size, and it is viewed through a focusing mirror. The cavity and focusing mirror are ideally maintained at the same temperature but differences of up to 1 C may exist, in which case a correction utilising the mirror emissivity can usefully be made. That emissivity has been measured at instrument level during pre-launch calibration by viewing an external target at the same temperature as the IFC while varying the calibration mirror temperature.
The techniques used to calibrate the field of view of the High
Resolution Dynamics Limb Sounder (HIRDLS) instrument and the results
of the calibration are presented. HIRDLS will be flown on the NASA EOS
Aura platform. Both in-field and out-of-field calibrations were
performed. The calibration results are compared to the requirements
and, in the case of out-of-field, mechanisms explaining the results