HAMP Instrumentation

 

The instrument suite HAMP (HALO Microwave Package) consists of a highly sensitive cloud radar and a suite of passive radiometers in different frequency bands. It was designed to bridge in situ measurements and satellite remote sensing by MPI-M in collaboration with the University Hamburg and the German Aerospace Center. This unique combination of active and passive sensors will helps to remove many of the ambiguities inherent in approaches employing pure passive or active remote sensing techniques. While radars provide excellent spatial resolution but only ambiguous information on the microphysical conditions in the sampled volume, radiometers have only poor or no spatial resolution but deliver integral constraints in the observed column as for example the liquid water path or ice/water partitioning. Thus the information provided by these active and passive sensors is largely complementary [1].

 

Cloud Radar
The cloud radar that is part of HAMP is a MIRA36 and operates at 35.5 GHz. The cloud radar is provided by the University Hamburg. The most important difference to CloudSat (which is in orbit as part of the A-train satellite constellation since 2006) is the higher sensitivity, which is further aggravated by higher attenuation at 94 GHz. While CloudSat can only detect drizzling or raining clouds, the airborne measurements also capture a significant fraction of non-precipitating cloud types. The finer spatial resolution and polarization measurements is another benefit of airborne cloud observations.


Radiometers
Microwave radiometers sampling at a selected variety of attenuated and window-frequencies are also part of HAMP. Over ocean lower frequencies are used for the observation of clouds and rain. Thereby information can be gained from the emission signal of the liquid hydrometeors in contrast to the low emissivity of the ocean background. Due to the high emissivity of land surfaces, emission based methods are not applicable for hydrometeor observations over land. There higher frequencies (> 85 GHz) sensitive to scattering at frozen hydrometeors need to be applied. To perform observations over ocean and land HAMP includes frequencies between 22 and 183 GHz. The specific frequencies were selected to match those of the AMSU A and B sounders. The high frequency channel, for the purpose of rainfall retrieval over land was centered at the 118 GHz O2 absorption following a suggestion of [2].

1. Mech, M., Orlandi, E., Crewell, S., Ament, F., Hirsch, L., Hagen, M., Peters, G., Stevens, B. (2014): HAMP – the microwave package on the High Altitude and LOng range research aircraft (HALO), Atmos. Meas. Tech., DOI:10.5194/amt-7-4539-2014

2. Bauer, P. and Mugnai, A. (2003): Precipitation profile retrievals using temperature-sounding microwave observations. JGR Atmospheres, DOI:10.1029/2003JD003572