Dual POL Radiometer

|| Dual Polarized Radiometers RPG-DPR series

Introduction

The RPG-XCH-DP is a 2/3/4 frequency, dual polarisation radiometer with direct detection receivers and complete auto-calibration frontends. The system requires no external calibration targets and performs sky tippings for absolute calibration purposes. The system is split into different frequency modules which are grouped on top of a precision elevation / azimuth positioner. Therefore the antennas can reach every point in the sky and complicated scanning schemes, including full sky LWP / IWV maps are possible.
One of the key features is the measurement of polarisation difference (PD) during rain events under e.g. 30° elevation angle. Falling droplets are flattened due to the air resistance from below and nearly form an ellipsoid with long axis along the horizontal direction. Therefore the emission of falling droplets is more pronounced in the horizontal polarisation compared to the vertical. This allows for the separation of cloud liquid (perfectly round droplets, approx. 20 μm in diameter) and rain liquid. Without taking the polarisation difference into account, a radiometer overestimates the total liquid water content during rain by assuming that the brightness temperature signal is all generated by small cloud droplets. The small cloud droplets produce a much lower sky temperature than the bigger rain droplets, even with the same amount of liquid water. Therefore the rain droplet contribution to the sky temperature is relatively large while their contribution to the total liquid is smaller.

Applications

  •  Soil moisture measurements
  •  Rain observations
  •  Discrimination of Cloud Liquid (LWC) and Rain Liquid (LWR)
  •  Accurate LWP measurements during rain events
  •  Cloud physics and structure LWP
  •  (Liquid Water Path)
  •  IWV (Integrated Water Vapour)
  •  Full sky IWV / LWP mapping
  •  Cloud coverage

Polarization Difference for rain and cloud mixtures

Polarization Difference for rain and cloud mixtures

simple regression retrieval for rain and cloud fraction of LWP

simple regression retrieval for rain and cloud fraction of LWP