NASA's integrated Instrument Simulator Suite for Atmospheric Remote Sensing from spaceborne platform (ISSARS) and its role for the GPM mission

Forward simulation is an indispensable tool for evaluation of precipitation retrieval algorithms as well as for studying snow/ice microphysics and their radiative properties. The main challenge of the implementation arises due to the size of the problem domain. To overcome this hurdle, assumptions need to be made to simplify complex cloud microphysics. It is important that these assumptions are applied consistently throughout the simulation process. ISSARS addresses this issue by providing a computationally efficient and modular framework that can integrate currently existing models and also capable of expanding for future development. ISSARS is designed to accommodate the simulation need for GPM’s radar and microwave imager as well as optical instruments such as lidars and polarimeters that will be included in future missions. ISSARS’s computation is performed in three stages: input reconditioning, electromagnetic properties calculation, and instrument simulation. The computation is implemented as a web service while its configuration can be accessed through a web-based interface. Input Reconditioning Module (IRM) uses geophysical properties of the atmosphere and the background earth surface forecasted by various numerical models (e.g. WRF, DHARMA, and LIS), applies atmospheric microphysics assumptions as specified by users, and produces location centric description of atmospheric/surface constituents. The users are allowed to use the existing constraints as reported by the models, provide the default values for the parameters that are not specified by the models, and/or override the assumptions used by the models. These customized parameters will be applied consistently across all stages of ISSARS’ computation. At the second stage of computation, Scattering Emission and Absorption Modules (SEAMs) computes the electromagnetic characteristics of the cloud particles and the background surface. The calculation parameters can also be customized by the users. The product of this stage, which is also location centric, becomes an input for the last stage, Instrument Simulator Modules (implementation is currently in progress). This presentation will demonstrate configuration procedures, illustrate some sample intermediate outputs of the IRM and SEAMs with an emphasis on the role of ISSARS for the GPM mission