Model Estimation of the HIRDLS Exit Aperture Fractional Open Area

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument suffered a, debilitating event during file Aura Satellite launch on July 15, 2004. After the, initial instrument activation phase was completed 25 days later, the first atmospheric scan tests revealed a much different radiance field than was expected prior to launch. A subsequent. lengthy, investigation suggested that the HIRDLS exit aperture was mostly obstructed by sheathing material that lined the inner fore-optics cavity. As part of the radiance correction process workaround. if, is necessary to provide radiances to the retrieval algorithm Chat are equivalently unobstructed (clear view), hence, knowledge on the amount, of unobstructed exit-aperture area is needed. This manuscript describes the problem and the modeling method used to estimate the amount of unobstructed area, of the HIRDLS exit aperture. Particular emphasis will be given to the type of data required to ascertain this quantity. Lastly, a diagnostic scheme for evaluating the calculated unobstructed open area for each channel will be discussed, along with a look to the future.