B021-0003
GEDI Precision Positioning Performance

Tuesday, 8 December 2020
Poster
Taylor Thomas, Emergent Space Technologies, Laurel, MD, United States, Scott B Luthcke, NASA Goddard Space Flight Center, Geodesy and Geophysics Lab, Greenbelt, MD, United States, David D Rowlands, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Joseph B Nicholas, Emergent Space Technologies, Inc @ NASA GSFC Geodesy and Geophysics Lab, Greenbelt, MD, United States and Teresa Pennington, KBRWyle, Denver, NC, United States
Abstract:
GEDI Precision Positioning Performance

The Global Ecosystem Dynamics Investigation (GEDI) mission launched from Cape Canaveral, Florida on December 5th, 2018, with the goal of providing the first global, high-resolution observations of forest vertical structure. The fundamental measurement used to achieve mission science objectives is the geolocation of individual waveforms collected by the GEDI lidar instrument. Geolocation is computed as a function of three complex measurements: (1) the position of the laser altimeter in inertial space, (2) the pointing of the eight individual lidar beams, and (3) the laser pulse round-trip range estimate computed from the waveform processing. GEDI Precision Positioning computes the first of these; the precise position of the laser altimeter instrument.

The GEDI payload is berthed onboard the International Space Station (ISS) at the Japanese Experiment Module (JEM) Exposed Facility Unit (EFU) #6 location. The payload includes a TriG GPS receiver developed by NASA’s Jet Propulsion Laboratory (JPL) and manufactured by MOOG as the follow-on to the proven high-performance BlackJack series of space geodetic GPS receivers. Tracking data collected by the GPS receiver is the primary data source used for generating positioning solutions. Positioning is performed using GEODYN, NASA Goddard Space Flight Center’s state-of-the-art orbit determination and geodetic parameter estimation software, employing a reduced-dynamic solution strategy.

Here we discuss the challenges associated with computing high accuracy geodetic positioning solutions for the GEDI altimeter instrument, including GPS signal blockages due to surrounding ISS structures and the lack of an independent validation data source such as satellite laser ranging (SLR) data. Early mission precision positioning performance is assessed by analyzing GPS observable residuals, solution precision, and comparisons to ISS NRT solutions. In addition, we examine filtered GEDI altimeter data residual performance for an independent assessment of positioning. We discuss the positioning performance impact on the overall geolocation performance of the altimeter surface returns. Finally, we discuss future positioning improvements and their impact on geolocation.

<< Previous Abstract | Next Abstract >>