ROTATING UNIVERSAL RADIOMETER FOR PLANETARY BOUNDARY LAYER OBSERVATIONS AND LAND-ATMOSPHERE INTERACTIONS

M. Eble¹, M. Klein¹

¹Boulder Environmental Sciences and Technology

Around to 40% of the Forecast Sensitivity to Observation Impact (FSOI) is provided by space based passive microwave humidity and temperature measuring sensors (Geer, et al., 2019). All other observations (e.g. infrared sensors, radiosondes, surface stations, ships, and buoys) provide the remaining 60%. Many other papers have documented the importance of radiometer observations for short term and long term weather forecasting.

There is more that passive microwave sensors could provide. A number of papers also examine the impact of adding more of these sensors on orbit, e.g., (Duncan, Bormann, & Holm, 2021), (Rivoire, et al., 2024). All of the studies confirm that more radiometer sensors on orbit will provide a significant positive impact on numerical weather prediction (NWP) model errors.

Many papers have also described the benefits of hyperspectral microwave sensors and how this approach to sensor design can further improve observations, e.g., (Boukabara & Garrett, 2011), (Maddy, Iturbe-Sanchez, & Boukabara, 2024).

While much of the current work focuses on space based sensors, ground based microwave radiometers also have the potential for improving atmospheric observations, especially in the atmospheric boundary layer. However, the ground based microwave radiometer technology currently in use is at least 40 years old. Sensor electronics might have improved during past decades, but not observational capabilities. Ground based radiometers are still using a rotating mirror, with two frequency bands (e.g. 20-30 and 50-58 GHz) mix polarizations in their observations, and they require regular liquid nitrogen calibration by a Ph.D. level operator.

We will describe a sensor known as the Rotating Universal Radiometer (RUR). This constantly rotating sensor can observe in dual polarizations, cover a wide frequency range, e.g., 6 to 220 GHz, and provide hyperspectral benefits, all in one integrated, rugged, IP67 sealed instrument that calibrates autonomously and reduces the need for user intervention. In addition to providing humidity and temperature profiles with much improved vertical resolution within the atmospheric boundary layer, the RUR sensor can also observe during precipitation events, thus enabling the measurement of precipitation rates. The sensor is capable of operating from a buoy without requiring platform stabilization. The RUR sensor can also perform simultaneous measurements of the surface below the sensor (land or ocean) and the atmosphere, thus providing valuable information for analyzing the interactions between these two regimes.

We will present the simulated capabilities of the RUR sensor for temperature and humidity profiling in the atmospheric boundary layer and further aloft. Simulated retrievals have shown significant improvements to retrieval accuracy over the current ground based technology.

References

Boukabara, S. A., & Garrett, K. (2011). Benefits of a Hyperspectral Microwave Sensor. 2011 IEEE Sensors (pp. 1881-1884). Limerick, Ireland: IEEE.

Duncan, D. I., Bormann, N., & Holm, E. V. (2021). On the addition of microwave sounders and numerical weather prediction skill. Quarterly Journal of the Royal Meteorological Society, 3703-3718. doi:10.1002/qj.4149

Geer, A., Bormann, N., Lonitz, K., Weston, P., Forbes, R., & English, S. (2019, October). Recent progress in all-sky radiance assimilation. ECMWF Newsletter. Retrieved February 18, 2023, from https://www.ecmwf.int/en/newsletter/161/meteorology/recent-progress-all-sky-radiance-assimilation

Maddy, E. S., Iturbe-Sanchez, F., & Boukabara, S. A. (2024). Toward the Next Generation of Microwave Sounders: Benefits of a Low-Earth Orbit Hyperspectral Microwave Instrument in All-Weather Conditions Using AI. IEEE Journal of selected topics in applied Earth observations and remote sensing, 4235-4245. doi:10.1109/JSTARS.2024.3356858

Rivoire, L., Marty, R., Carrel-Billiard, T., Chambon, P., Fourrie, N., Audouin, O., … Ackermann, J. (2024). A global observing-system simulation experiment for the EPS–Sterna microwave constellation. Quarterly Journal of the Royal Meteorological Society, 2991-3012. doi:10.1002/qj.4747