Forecasting the Future of Weather-Prediction Satellites

The International Radio Occultation Working Group COSMIC2/FORMOSAT meeting kicked off recently in Boulder, CO, at the University Corporation for Atmospheric Research. (Despite what you may think, while radio occultation is used to predict the weather, it's a scientific process, and there was nary a Ouija Board in the place.)

Radio occultation (RO) is a technique for gleaning information about a medium (in this case, the Earth's atmosphere) by measuring how radio waves are refracted through that medium. The current satellite constellations that return radio occultation data are in low-earth orbit (LEO). Each satellite watches its horizon for global positioning satellites (also known as global navigation satellite systems or GNSS satellites.) Due to the nature of their tasks, global positioning satellite orbits are very precisely known. When an RO satellite observes a GNSS satellite rise over the horizon of the Earth, it compares the known position of the satellite to the position returned by an array of antennas on the radio occultation vehicle that detected the GNSS satellite's signals, assuming straight line propagation. The difference in the observed straight-line position compared with the precisely known actual position of the GNSS vehicle at that time can be used to derive the refraction of radio waves through the intervening atmosphere.¹ With information about the index of refractivity reported back by the RO constellations, computers on the ground can derive various atmospheric quantities at the time of the observation including the temperature, moisture content of the atmosphere, wind speeds, and barometric pressure. These numbers, aggregated on a global basis, are used for weather forecasting. 

Related:Low-Earth-Orbit Satellites Must Minimize Astronomical Interference

On the space weather side of things, the RO satellites can report accurate information on the height and critical frequency of the ionosphere's F2 layer, the layer that enables ground-station-to-ground-station skip-radio propagation and inhibits satellite-to-ground-station radio propagation.

For a fun read on these two types of propagation and rocket-borne experiments, the US government ran to influence them artificially in two different eras. (See Project Smoke Puff [1950s focus on ionospheric skip from ground-to-ground stations] and Dr. Natasha Jackson and Samarium Pink Clouds [2010s focus on satellite to ground stations.]

With COSMIC2 at mission's end, the working group met to formulate plans for the next generation satellite constellation which, as it turns out, may be a completely commercial affair.

Related:This Satellite Will Fix Existing Satellites in Space

Commercial data providers for radio occultation data

While the National Science Foundation funded both the COSMIC and COSMIC2 radio occultation missions, there are now three commercial ventures—Spire, PlanetiQ, and Muon Space—that are supplying radio occultation data to the National Oceanic and Atmospheric Administration (NOAA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT.) Each of these companies launched their satellite constellations aboard SpaceX rockets over the last several years. The corporations presented their recent findings at the working group meeting along with some information about how NOAA, EUMETSAT, and other agencies around the world are using their data. All the slide decks for the working group including the full slide decks for the three commercial data vendors can be found here. One of the questions now facing radio occultation scientists and analysts is whether or not the entire radio occultation mission will fall to purely commercial venues and whether the data they provide will be good enough.

Radio occultation data availability & geopolitical military conflicts

One fascinating outcome of the study of available radio occultation data beyond terrestrial and space weather predictions involved the influence of military conflicts on data availability. Interestingly, the presented talk had nothing to do with ground stations, but rather with GPS-jamming technologies. The talk itself did not posit a cause for radio frequency interference loss of RO measurements, but it did point out that the highest density of lost packets occurred over the Ukraine over the period of the data collected by the study's scientists. You can review the entire slide deck here.

Related:The 3DP Satellite Market Will Hit $1B by 2034

Reading even more about radio occultation

In addition to the talks presented at the working group, there were over 100 posters presented in two poster sessions. The posters can be perused from the comfort of your screen here.

Reference