Visualising Phenomena Virtually Unobservable by Current Satellite Instruments

Optical Surfaces Ltd. has supplied key reference testing optics for the HIRDLS (High Resolution Dynamics Limb Sounder) Instrument to the University of Oxford (UK).

For many years, the University of Oxford has been a leading international research centre and developer of satellite instruments in the fields of atmospheric, oceanic and planetary physics.

As a joint collaboration between companies in the United States of America and the United Kingdom, HIRDLS is an advanced new instrument that is due to fly on NASA's 'Earth Observing System' satellite called AURA around the spring of 2004. It will measure stratospheric and mesospheric temperature and composition at unprecedented high spatial resolution, revealing processes that are virtually unobservable by current satellite instruments. Atmospheric, Oceanic and Planetary Physics at the University of Oxford has a major role in its design and construction, including responsibility for its calibration, flight operations and science data analysis.

To provide a reference wavefront to verify the performance of the HIRDLS Instrument’s Optical Bench Assembly (OBA) required Optical Surfaces Ltd. to produce a large ultra-smooth off-axis paraboloid of 1352mm focal length and steep 15-degree off-axis angle. Using proprietary production techniques Optical Surfaces achieved a uniform lambda/8 p-v at 633 nm finish across the surface of the 305mm diameter off-axis paraboloid.

The off-axis paraboloid was supplied mounted and tested after coating in clean room conditions to meet with the rigorous demands of space borne optical instruments. Production is approved to ISO 9002 and all high precision optics and systems leaving the Optical Surfaces Ltd. production facility are quality certified by topographic and interferometric analysis.

The scientific aims of HIRDLS will be to measure temperature, trace chemicals, and geopotential height gradients in order to understand better the chemistry and dynamics of the Earth’s stratosphere and mesosphere that are important to climate change. The HIRDLS instrument has a better vertical resolution than previous limb sounder instruments, because of its smaller field of view, and the horizontal spacing between the profiles is much close because the instrument is able to scan in azimuth.

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