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Proceedings Paper

Global Ecosystem Dynamics Investigation (GEDI) instrument alignment and test
Author(s): Bente Eegholm; Shane Wake; Zachary Denny; Pete Dogoda; Demetrios Poulios; Barry Coyle; Pete Mulé; John Hagopian; Patrick Thompson; Luis Ramos-Izquierdo; Bryan Blair
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Paper Abstract

NASA’s Global Ecosystem Dynamics Investigation (GEDI) instrument was launched Dec. 5, 2018, and installed on the International Space Station 419 km from Earth. The GEDI is a Light Detection and Ranging (LIDAR) instrument; measuring the time of flight of transmitted laser beams to the Earth and back to determine altitude for geospatial mapping of forest canopy heights. The need for very dense cross track sampling for slope measurements of canopy height is accomplished by using three individual laser transmitter systems, where each beam is split into two beams by a birefringent crystal. Furthermore, one transmitter is equipped with a diffractive optical element splitting the two beams into four, for a total of 8 beams. The beams are reflected off of the features and imaged by an 800 mm diameter Receiver Telescope Assembly, composed of a Ritchey-Chrétien telescope, a refractive aft optics assembly and focal plane array which collects and focuses the light from the 8 probe beams into the 8 science fibers, each with a field of view on the Earth subtending 300 μrad. The dense cross-track sampling mandated a custom designed dual-fiber interface. The science fibers had to be aligned to the nominal, projected laser spots. The alignment was highly dependent on optimization and co-positioning of the fibers pair-wise due to mechanical constraints. This paper presents the end-to-end alignment and metrology of the full optical system from transmitter elements through receiver telescope, aft-optics, focal plane and receiver fibers performed at NASA Goddard Space Flight Center.

Paper Details

Date Published: 30 August 2019
PDF: 18 pages
Proc. SPIE 11103, Optical Modeling and System Alignment, 1110308 (30 August 2019); doi: 10.1117/12.2532471
Show Author Affiliations
Bente Eegholm, NASA Goddard Space Flight Ctr. (United States)
Shane Wake, NASA Goddard Space Flight Ctr. (United States)
Zachary Denny, Science Systems and Applications, Inc. (United States)
Pete Dogoda, Sigma Space Corp. (United States)
Demetrios Poulios, American Univ. (United States)
Barry Coyle, NASA Goddard Space Flight Ctr. (United States)
Pete Mulé, NASA Goddard Space Flight Ctr. (United States)
John Hagopian, ATA Aerospace, LLC (United States)
Patrick Thompson, NASA Goddard Space Flight Ctr. (United States)
Luis Ramos-Izquierdo, NASA Goddard Space Flight Ctr. (United States)
Bryan Blair, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 11103:
Optical Modeling and System Alignment
Mark A. Kahan; José Sasián; Richard N. Youngworth, Editor(s)

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