An alternative algorithm is being analyzed to retrieve ozone and aerosol vertical distribution information from the
OMPS/LP sensor which will be manifested on the upcoming NPOESS Preparatory Project (NPP) platform in early 2011.
The algorithm relies on the optimal estimation method to infer ozone density and aerosol extinction directly from the
radiance measurements made by the ensemble of CCD array pixels. The fundamentals of the technique are reviewed and
the advantages of the method with respect to the mainstream retrieval algorithm are discussed. Sample results are given
to illustrate the performance of the new method.
The High Resolution Dynamics Limb Sounder (HIRDLS) instrument suffered a debilitating event during the Aura
Satellite launch on July 15, 2004. After the initial instrument activation phase was completed 25 days later,
the first atmospheric scan tests revealed a much different radiance field than was expected prior to launch. A
subsequent lengthy investigation suggested that the HIRDLS exit aperture was mostly obstructed by sheathing
material that lined the inner fore-optics cavity. As part of the radiance correction process workaround, it is
necessary to provide radiances to the retrieval algorithm that are equivalently unobstructed (clear view); hence,
knowledge on the amount of unobstructed exit-aperture area is needed. This manuscript describes the problem
and the modeling method used to estimate the amount of unobstructed area of the HIRDLS exit aperture.
Particular emphasis will be given to the type of data required to ascertain this quantity. Lastly, a diagnostic
scheme for evaluating the calculated unobstructed open area for each channel will be discussed, along with a
look to the future.
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) flight
instrument, which is currently in orbit on the NASA Aura Satellite,
went through a pre-launch calibration at Oxford University during
Autumn 2002. One of the calibration exercises was to characterize the radiometric signals of the HIRDLS proto-flight model (PFM). It was discovered during the data-analysis phase, that the radiometric data required special treatment. Because of the stringent radiometric requirements imposed on HIRDLS, these additional analyses were necessary. This manuscript will detail these specific analysis techniques that were used on the data and present results based on a full analysis of the data, including a complete accounting of the statistical error analysis.
A pre-launch calibration of the High Resolution Dynamics Limb Sounder (HIRDLS) flight instrument was performed at Oxford University in Fall 2002. The in-band spectral characterization was performed was performed as part of this exercise. Spectral response data for all 21 channels were obtained for three different experimental conditions (nominal and two off-nominal operating conditions). Results from these data sets will be presented, as well as the analysis procedures used, along with a discussion on error analysis.
Results from a pre-launch in-band spectral characterization of the 21-channel HIRDLS flight instrument will be presented. These data were obtained during a pre-launch calibration of HIRDLS at Oxford University (Fall 2002). A monochromator, equipped with a controllable diffraction grating, was used to produce monochromatic light for these tests. The monochromator was enclosed, with HIRDLS, in a large vacuum chamber. The monochromator was also equipped with a polarizer, which allowed for data to be procured at known orthogonal polarizations for each channel. A calibration detector, with a flat spectral response, was used to monitor the output from the monochromaotr. This report will consist of a description of the analyiss methodlogy, leading to an unpolarized instrument spectral response function for each channel.
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.
Results from a pre-launch radiometric calibration of the 21-channel HIRDLS instrument will be presented. These data were obtained during a pre-launch calibration of HIRDLS at Oxford University (Fall 2002). Two external blackbody cavities were used to generate temperatures between ~90 K to ~320 K. These blackbodies were located, along with HIRDLS, inside a large vacuum chamber. Data were taken at three different focal-plane temperatures (61 K, 66 K, and 71 K). This paper will cover a variety of details; such as, data--taking procedures, analysis methodology, and the resulting linearity analyses.