28 Nov 2022
28 Nov 2022
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Efficient Collocation of GNSS Radio Occultation Soundings with Passive Nadir Microwave Soundings

Alex Meredith1, Stephen S. Leroy2, and Kerri Cahoy1 Alex Meredith et al.
  • 1Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 2Atmospheric and Environmental Research, Lexington, MA 02421, USA

Abstract. Radio Occultation (RO) using the Global Navigation Satellite Systems (GNSS) can be used to infer atmospheric profiles of microwave refractivity in the Earth’s atmosphere. GNSS RO data are now assimilated into numerical weather prediction models and used for climate monitoring. New remote sensing applications are being considered that fuse GNSS RO soundings and passive nadir-scanned radiance soundings. Collocating RO soundings and nadir-scanned radiance soundings, however, is computationally expensive, especially as new commercial GNSS RO constellations greatly increase the number of global daily RO soundings. This paper develops a new and efficient technique, called the “rotation-collocation-method”, for collocating RO and nadir-scanned radiance soundings in which all soundings are rotated into the time-dependent reference frame in which the nadir sounder’s scan pattern is stationary. Collocations with RO soundings are then found when the track of an RO sounding crosses the line corresponding to the nadir sounder’s scan pattern. When applied to finding collocations between RO soundings from COSMIC-2, Metop-B-GRAS, and Metop-C-GRAS and the passive microwave soundings of ATMS on NOAA-20, Suomi-NPP, and AMSU-A on Metop-B and Metop-C for the month of January, 2021, the rotation- collocation method proves to be 99.0 % accurate and is hundreds to thousands of times faster than traditional approaches to finding collocations.

Alex Meredith et al.

Status: open (until 25 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1266', Anonymous Referee #1, 05 Jan 2023 reply
  • RC2: 'Comment on egusphere-2022-1266', Anonymous Referee #2, 25 Jan 2023 reply

Alex Meredith et al.

Model code and software

Software for Efficient Collocation-Finding Alex Meredith, Stephen Leroy, Kerri Cahoy

Alex Meredith et al.


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Short summary
We developed a new efficient algorithm leveraging orbital dynamics to collocate radio occultation soundings with microwave radiance soundings. This new algorithm is 99 % accurate and is much faster than traditional collocation-finding approaches. Speeding up collocation-finding is useful for calibrating and validating microwave radiometers and for data assimilation into numerical weather prediction models. Our algorithm can also be used to predict collocation yield for new satellite missions.