PlanetiQ Initial Precipitation Observations via Dual Linear Polarization Radio Occultation Measurements

The Radio Occultation Heavy Precipitation (ROHP) experiment on the Spanish PAZ mission has demonstrated the ability to measure heavy precipitation and snowfall from dual linear polarization GNSS radio occultation (RO) measurements. The key observable is the difference between the phase of the horizontal and vertical polarization components of the GNSS signals where the horizontal component of the signal is slowed slightly more by flattened hydrometeors than is the vertically polarized signal. These Pol-RO observations provide unique vertical profiles of precipitation that complement other methods of measuring precipitation.

Our 5^th PlanetiQ satellite launched August 16, 2024 and carries a dual linear polarization, high gain antenna for making polarized RO and surface reflection measurements, in addition to the standard RO measurements. This satellite will provide approximately 1100 Pol-RO profiles per day. Our 6^th satellite, scheduled to launch February 2025, will also carry such an antenna and double the Pol-RO per day to 2200. Our dual linear phase measurements are made with higher SNR than previous dual linear polarization RO measurements and have a better local multipath environment than PAZ and thus may provide the best Pol-RO performance yet achieved.

We will present an overview of our calibration and retrieval process to isolate the precipitation induced signatures. We will present our initial differential phase results, including determining the noise floor when no precipitation is present and comparisons with other collocated precipitation measurements and analyses such as ERA5 snowfall which has been shown to correlate with the PAZ measurements.

We will provide an initial assessment of how the sensitivity and performance depends on SNR and other factors and the degree to which higher SNR enables detection of smaller amounts of precipitation and certain clouds types such as anvil clouds. We will also present a summary of performance over land versus ocean and demonstrate the insensitivity of these measurements to variations in surface conditions and emissivity below that enable these observations to provide truly global coverage.