On May 8, the National Geospatial-Intelligence Agency (NGA) released Topic 3 of the Boosting Innovative GEOINT Science and Technology (BIG-ST) broad agency announcement. Topic 3 is Very Long Baseline Interferometry with Global Navigational Satellite Systems Capabilities (VLBI+G) Radio Telescope Signal Chain Development. Questions are due by 5:00 p.m. Eastern on May 15, and abstracts are due by 5:00 p.m. Eastern on May 31. Proposals are due by 5:00 p.m. Eastern on July 9.
This topic call seeks to develop an enhanced VLBI+G signal chain capability that can work in a network of existing VLBI systems to collect observations useful in supporting production of the Terrestrial Reference Frame (TRF) and Earth Orientation Parameters (EOP).
The VLBI+G signal chain capability shall be installed and tested in a Calian 12-meter radio telescope. If the prototype OT is successful, production version may call for installation on a General Dynamics 14-meter antenna.
The Geodesy mission of NGA’s Mapping, Charting and Geodesy (MC&G) domain is to better understand the earth to improve navigation, mapping, charting, tides, and geodetic products as called out in U.S. Code Title 10. To address this mission, NGA created the World Geodetic System (WGS). NGA’s WGS is a system of geodetic systems; at its heart is the TRF.
Geodesy is a science that studies the size, shape, gravitational field, motion, and orientation of the earth in space. Geodesy also analyzes the listed properties change over time relative to the stars and their individual gravitational fields. The earth’s orientation and motion through space is defined relative to the stars that are in the celestial sphere. A location on this celestial sphere is defined in terms of its coordinates in the Celestial Reference Frame (CRF), similar to the earth’s latitude and longitude system used to plot positions within the TRF.
The TRF is generated through accurately determined coordinates of a set of reference stations. It starts at the center of mass of our planet, while the coordinates of the reference stations implicitly define the scale of the TRF and the orientation of its axes. Since the earth is a dynamic planet with constantly moving continental plates, the TRF must be monitored and maintained as our planet changes.
VLBI uses observations of two or more radio telescopes observing the same very distant quasars (i.e., extremely luminous active galactic nucleus) to determine the orientation of the baseline between the telescopes with respect to the quasars to determine the EOP that define the relationship between the TRF and the CRF. These VLBI observations can also be used in the defining of the TRF’s scale. While Global Navigation Satellite Systems (GNSS) were principally designed to aid navigation and positioning, GNSS satellites can also be used in monitoring the earth’s polar motion, two of the EOP parameters.
Review NGA’s BIG-ST BAA Topic 3.
Source: SAM
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