Evaluation of radar multiple scattering effects inCloudsat configuration

[摘要] MonteCarlo simulationshave been performedto evaluate the importance ofmultiple scattering effects in co- and cross-polar radar returnsfor 94 GHz radars in Cloudsat and airborne configurations.Thousands of vertically structured profiles derived from some differentcloud resolving models are used as a test-bed. Mie theoryis used to derive the single scattering properties of the atmospherichydrometeors.Multiple scattering effects in the co-polar channel (reflectivityenhancement) are particularly elusive, especially inairborne configuration. They can bequite consistent in satellite configurations, like CloudSat,especiallyin regions of high attenuation and inthe presence of highly forward scattering layers associated withsnow and graupelparticles.When the cross polar returns are analysed [but note thatCloudSat does notmeasure any linear depolarization ratio (LDR hereafter)], high LDR valuesappear both in space and in airborne configurations.The LDR signatures are footprints ofmultiple scattering effects;although depolarization values as high as −5 dBcan be generated including non-spherical particles insingle scattering modelling,multiple scattering computations can produce values closeto complete depolarization (i.e. LDR=0 dB).Our simulated LDR profiles from an air-borne platformwell reproduce, in a simple frame,some experimental observations collected during the Wakasa Bay experiment.Since LDR instrumentaluncertainties were not positively accounted for during that experiment,more focused campaigns with air-borne polarimetric radarare recommended.Multiple scattering effects can be important for CloudSat applicationslike rainfall and snowfall retrievals sincesingle scattering based algorithmswill be otherwise burdened by positive biases.

[学科分类] 大气科学