LOMIRAD ULTRA-WIDEBAND LOW FREQUENCY RADIOMETER: PERFORMANCE ASSESSMENT AND PRELIMINARY FEEDBACK FROM MEASUREMENT CAMPAIGN

M. Brogioni¹, A. Lapini¹, A. V. Bosisio², M. Baldi¹, F. Montomoli¹, J. T. Johnson³, G. Macelloni¹

¹IFAC/National Research Council, Italy, 2IEIIT/National Research Council, Italy, 3Ohio State University

In the last decade, microwave ultra-wide band radiometry in the 0.4-2 GHz range has opened new frontiers for the remote sensing of natural surfaces [1] and especially for the cryosphere [2]. To date the only existing radiometer of this sort is the Ultra-Wideband Software-Defined Microwave Radiometer (UWBRAD) developed by The Ohio State University [3] and used in international campaigns both on the Arctic [4] and Antarctic [5]. The encouraging results of UWBRAD have motivated the scientific community to propose mission concepts to NASA and ESA, resulting in ESA’s 2024 selection of the CryoRad concept as a candidate for the Earth Explorer 12 program. To foster CryoRad’s development and to acquire new datasets, the Italian Space Agency – ASI funded the construction of an airborne UWB demonstrator called LoMiRad whose characteristics are reported in Table 1.

The radiometer samples the incoming radiation at a 122KHz spectral resolution and provides brightness temperature spectra internally calibrated with 4 reference loads (including active cold load and noise sources). The output data is a spectrum aggregated into sixteen 100 MHz subchannels with a minimum integration time of 100ms. Auxiliary instruments (e.g. IR and Video cameras, thermodynamic temperatures, attitude, GPS) further provide additional information needed to process the data and/or infer information on the observed targets. The fine spectral sampling of the signal allows for the detection and mitigation of radio frequency interference (RFI) given the instrument’s operation in non-protected bands. LoMiRad manufacturing and coding completed in December 2024, and calibration tests were performed indicating a linear behavior of the receiver for at least 100-500K input power levels, which corresponds to the range of the calibration sources. A four-hour acquisition performed with input matched loads placed in evaporating liquid nitrogen shows a precision of about 0.2K throughout the bandwidth for a 100ms integration time. The value drops to 0.15K for a 400ms integration. A test-site for sky calibration having low RFI levels was identified on the Tuscan Apennines (43.877682, 11.622038), where data were collected during Jan 2025.

LoMiRad was deployed in the CryoS4 (CryoRad Survey for Sea Surface Salinity) campaign at Baffin Bay in August 2025.

A full description of the instrument performance and feedback from the campaign will be provided at the conference.

Table I – Specification of LoMiRad

ACKNOWLEDGEMENTS

This activity has been funded in part by the Italian Space Agency – ASI, under the contact ASI CI-UOT-2018-24

REFERENCES

1. J. T. Johnson et al., “Microwave Radiometry at Frequencies From 500 to 1400 MHz: An Emerging Technology for Earth Observations,” in IEEE JSTARS, vol. 14, pp. 4894-4914, 2021, doi: 10.1109/JSTARS.2021.3073286.

2. Jezek KC et al.,(2022) A review of recent developments in low-frequency ultra-wideband microwave radiometry for studies of the cryosphere. Front. Earth Sci. 10:1029216. doi: 10.3389/feart.2022.1029216

3. M. J. Andrews et al., “The Ultrawideband Software-Defined Microwave Radiometer: Instrument Description and Initial Campaign Results,” in IEEE TGRS, vol. 56, no. 10, pp. 5923-5935, Oct. 2018, doi: 10.1109/TGRS.2018.2828604.

4. C. Yardim et al., “Greenland Ice Sheet Subsurface Temperature Estimation Using Ultrawideband Microwave Radiometry,” in IEEE TGRS, vol. 60, pp. 1-12, 2022, Art no. 4300312, doi: 10.1109/TGRS.2020.3043954.

5. Brogioni M. et al., Ice Sheet and Sea Ice Ultrawideband Microwave radiometric Airborne eXperiment (ISSIUMAX) in Antarctica: first results from Terra Nova, The Cryosphere, 17 255-278, https://doi.org/10.5194/tc-17-255-2023, 2023.