Microwave Radiometer – RPG-HATPRO (G5 Series)

The RPG-HATPRO G5 is a state-of-the-art, ground-based passive microwave radiometer designed for high-resolution atmospheric profiling. It operates in two frequency bands:

• K-band (22.24–31.40 GHz) for water vapor profiling
• V-band (51.26–58.00 GHz) for temperature profiling using the oxygen absorption spectrum

The instrument features 14 channels (7 in each band) and measures brightness temperatures at up to 1-second temporal resolution. It supports two operating modes:

• Zenith mode (Z-mode): Vertical pointing for continuous time series of atmospheric profiles
• Scanning mode (S-mode): Elevation scans from ~4° to 90° for boundary layer profiling
• In boundary layer mode, the radiometer performs a series of elevation scans (0°, 4.2°, 4.8°, 5.4°, 6.6°, 8.4°, 11.4°, 14.4°, 19.2°, and 30°) at 0° azimuth to obtain high-resolution temperature profiles. The user-defined integration time per angle ranges from 20 to 60 seconds, resulting in a total scan time of 2 to 6 minutes. During S-mode scanning, Z-mode observations are temporarily paused.

To retrieve atmospheric profiles from brightness temperature measurements, the radiative transfer equation is inverted using an artificial neural network (ANN) approach. The ANN was trained using radiosonde data from Abu Dhabi (UAE), Muscat (Oman), Dammam (Saudi Arabia), and ERA5 reanalysis data. Temperature and humidity profiles are retrieved every 5 minutes, from the surface up to 10 km above ground level, with vertical resolution better than 100 meters in the lower troposphere.

The system also provides estimates of cloud liquid water content using a relative humidity threshold method (95%). Key atmospheric quantities such as stability indices and boundary layer height can be derived from the retrieved profiles.

The system includes an Infrared Temperature Sensor (IRTS) operating in the 8–14 μm range, used to estimate cloud base height (CBH) and cloud liquid water. This sensor improves cloud transmittance assessments and enhances the accuracy of humidity profiles when combined with microwave observations.

The RPG-HATPRO is equipped with a blower and heating module to prevent dew or condensation during foggy conditions, making it ideally suited for fog monitoring and boundary layer studies.

Validation studies comparing MWR retrievals with radiosonde profiles from Abu Dhabi International Airport have been published in the Atmospheric Research (link: https://doi.org/10.1016/j.atmosres.2019.104652) journal.

Figure 1. Microwave Radiometer – RPG-HATPRO (G5 Series).