Robert E. J. Watkins

KMOS: assembly, integration and testing of three 0.8-2.5 micron spectrographs

KMOS is a second generation instrument in construction for use at the European Southern Observatory (ESO) Very Large Telescope (VLT). It operates in the near-infrared (0.8 to 2.5 microns) and employs 24 deployable, image slicing integral field units (IFUs) feeding three spectrographs. The spectrographs are designed and built by a partnership of the University of Oxford and Rutherford Appleton Laboratories (RAL). We describe the assembly, integration and alignment procedures involved in the construction of these spectrographs in detail. We also present the results of the cryogenic optical tests, including the first data taken through the full spectrograph optical train and the details of the test facility and procedures involved.

HIRDLS field-of-view calibration techniques and results

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 are discussed.

HIRDLS monochromator calibration equipment

A specially designed and built monochromator was developed for the spectral calibration of the HIRDLS instrument. The High Resolution Dynamics Limb Sounder (HIRDLS) is a precision infra-red remote sensing instrument with very tight requirements on the knowledge of the response to received radiation. A high performance, vacuum compatible monochromator, was developed with a wavelength range from 4 to 20 microns to encompass that of the HIRDLS instrument. The monochromator is integrated into a collimating system which is shared with a set of tiny broad band sources used for independent spatial response measurements (reported elsewhere). This paper describes the design and implementation of the monochromator and the performance obtained during the period of calibration of the HIRDLS instrument at Oxford University in 2002.

HIRDLS instrument radiometric calibration black body targets

The pre-launch calibration of the HIRDLS instrument took place in a dedicated facility at the University of Oxford. One aspect of this calibration was the determination of the response of the instrument to black body radiation. This was achieved with the use of purpose built full aperture black body targets which were mounted in the vacuum chamber together with all of the calibration equipment. Special attention was placed on the absolute knowledge of the emission from these targets. This was done through a combination of thermometric sensor calibration traceable to the International Temperature Standard (ITS-90), surface emission measurements, cavity design and modeling and controlling the stray light sources in the vacuum chamber. This paper describes the design requirements, implementation and performance achieved.

Prelaunch calibration of the NASA AURA HIRDLS instrument

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 Earths 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.

Spectral characterization of the HIRDLS flight instrument from prelaunch calibration data

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.

NASA AURA HIRDLS instrument calibration facility

A state-of-the-art calibration facility was designed and built for the calibration of the HIRDLS instrument at the University of Oxford, England. This paper describes the main features of the facility, the driving requirements and a summary of the performance that was achieved during the calibration. Specific technical requirements and a summary of the performance that was achieved during the calibration. Specific technical requirements and other constaints determined the design solutions that were adopted and the implementation methodology. The main features of the facility included a high performance clean room, vacuum chamber with thermal environmental control as well as the calibration sources. Particular attention was paid to maintenance of cleanliness (molecular and particulate), ESD control, mechanical isolation and high reliability. Schedule constraints required that all the calibration sources were integrated into the facility so that the number of re-press and warm up cycles was minimized and so that all the equipment could be operated at the same time.

Prelaunch Radiometric Calibration of the HIRDLS Flight Instrument: Results and Use in On-Orbit Data Processing

Results from the prelaunch radiometric calibration of the 21-channel High Resolution Dynamics Limb Sounder (HIRDLS) flight instrument are presented. The calibration was carried out in the Department of Physics of Oxford University. Two large aperture external blackbody cavities were used to generate stable radiances at target temperatures between ~90 and ~320 K. These blackbodies were located, along with the HIRDLS instrument, inside a large vacuum chamber. Data were taken at three different focal-plane temperatures (~61, ~66, and ~71 K). To complicate matters beyond the initial scope of the prelaunch calibration, a failure of some contamination close-out material (Kapton) that lined the inner fore-optics cavity occurred during launch, which made the original in-flight radiometric calibration procedure impossible. Accordingly, the radiometric conversion algorithm had to be changed, requiring more information from prelaunch calibration to be used than first envisioned. This paper discusses a variety of details, such as data-taking procedures, analysis methodology, associated error analyses, and necessary changes to the radiometric conversion algorithm needed for inflight data processing.

Stable Space‐Based Encapsulated Platinum Resistance Thermometry over the Range −9 °C to 50 °C

The High Resolution Dynamic Limb Sounder (HIRDLS) is a space‐based filter radiometer for atmospheric monitoring between the upper troposphere and the mesosphere. Retrievals of trace chemicals, temperature and geopotential height gradients will be obtained on a global scale. This radiometer uses the two point calibration algorithm in which the radiometer views a cold “zero radiance” space view, and a high‐emissivity warm blackbody target, of known temperature. To achieve a high radiometric performance, an accurate thermometry system is used to measure cavity temperature over the range −9 °C to +50 °C allowing the instrument’s gain to be measured as required (nominally every 66 seconds). The thermometry error budget for the cavity allows a temperature sensor stability of 25 mK over the mission lifetime of five years in‐flight and two years before instrument launch. This high thermometry performance is achieved using two redundant sets of three platinum resistance thermometers (PRTs) to sense the cavity temp...

Radiometric calibration of the HIRDLS flight instrument from prelaunch calibration data

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.