Three-way calibration checks using ground-based, ship-based, and spaceborne radars

Abstract

Abstract. This study uses ship-based weather radar observations collected from research vessel Investigator to evaluate the Australian weather radar network calibration monitoring technique that uses spaceborne radar observations from the NASA Global Precipitation Mission (GPM). Quantitative operational applications such as rainfall and hail nowcasting require a calibration accuracy of ±1 dB for radars of the Australian network covering capital cities. Seven ground-based radars along the western coast of Australia and the ship-based OceanPOL radar are first calibrated independently using GPM radar overpasses over a 3-month period. The calibration difference between the OceanPOL radar (used as a moving reference for the second step of the study) and each of the seven operational radars is then estimated using collocated, gridded, radar observations to quantify the accuracy of the GPM technique. For all seven radars the calibration difference with the ship radar lies within ±0.5 dB, therefore fulfilling the 1 dB requirement. This result validates the concept of using the GPM spaceborne radar observations to calibrate national weather radar networks (provided that the spaceborne radar maintains a high calibration accuracy). The analysis of the day-to-day and hourly variability of calibration differences between the OceanPOL and Darwin (Berrimah) radars also demonstrates that quantitative comparisons of gridded radar observations can accurately track daily and hourly calibration differences between pairs of operational radars with overlapping coverage (daily and hourly standard deviations of ∼ 0.3 and ∼ 1 dB, respectively).

Characterizing Precipitation and Improving Rainfall Estimates Over the Southern Ocean Using Ship‐Borne Disdrometer and Dual‐Polarimetric C‐Band Radar

“…OceanPOL has a beamwidth of 1.3°, a range sampling of 125 m (pulse length of 1 microsecond), and a maximum radial distance of 150 km. It typically scans about 14 elevation angles from 0.7° to 32° at 1° azimuth intervals every 6 min (Protat et al., 2022), but the numbers of elevation angles and sampling intervals vary between cruises. The antenna control system of OceanPOL is used to stabilize the antenna for the radar to operate on a ship.…”

“…The OceanPOL calibration follows the framework applied to operational radars in Australia (Protat et al., 2022; Warren et al., 2018). However, we implemented an additional quality control step to the PPI data to remove, to the extent possible, non‐meteorological signals (e.g., sea clutter signals), as well as a Z DR calibration adjustment of −0.4 dB based on our initial analysis of multiple stratiform cases (not shown).…”

“…The RV Investigator carries a dual‐polarization C‐band (5.5 GHz) weather radar called OceanPOL, one of only three ship‐borne dual‐polarization weather radars in the world and the only one operating over the SO (Protat et al., 2022). OceanPOL provides high‐resolution 3‐D measurements of precipitation at multiple elevation angles, and its dual‐polarization capability enables improved retrievals of hydrometeor species and spatial distributions.…”