We have studied an alternative approach, direct assimilation of the Level 1a DDM product into a 2-dimensional, Variational vector wind Analysis Method (VAM). Through working at a data product much closer to the signal actually captured by the instrument, assimilation offers the potential to incorporating a representation of the instrument response into the cost function itself, rather than attempting to remove these effects through calibration. Furthermore, this method will extract information from multiple “looks” at the same specular point, making better use of data that would otherwise have been discarded.
An operator (consisting of the forward model and Jacobian) have been derived for the CYGNSS DDM Level 1a product. Early comparisons with a CYGNSS Level 1a data, obtained around several Tropical Storms, covering conditions of moderate (~ 8m/s) and high (~40 m/s) wind speeds, and exhibiting nearly symmetric as well as highly asymmetric functional shapes, have shown good agreement. A closed-form representation of the Jacobian has been derived, and shown to agree with finite difference tests. Integration of this model into existing VAM code has begun, and we expect to present the status of those experiments at the meeting, along with an assessment of the expected quality of the resulting wind product. A draft Interface Control Document (ICD) defining the model state variables and meta data has been prepared, to further future utilization of the operator.