Remote Sensing of Liquid Water and Ice Cloud Optical hickness and Effective Radius in the Application of Airborne Multispectral MAS Data

A multispectral scanning spectrometer was used to obtain measurements of the bidirectional Areflectance and brightness temperature of clouds, sea ice, snow, and tundra surfaces at 50 discrete wavelengths between 0.47 and 14.0 (mu)m. These observations were obtained from the ANASA ER-2 aircraft as part of the First ISCCP (International Satellite Cloud Climatology AProject) Regional Experiment (FIRE) Arctic Clouds Experiment, conducted over a 1600 km × A500 km region of the north slope of Alaska and surrounding Beaufort and Chukchi Seas Abetween 18 May and 6 June 1998. Multispectral images in eight distinct bands of the AModerate Resolution Imaging Spectroradiometer (MODIS) Airborne Simulator (MAS) were used Ato derive a confidence in clear sky (or alternatively the probability of cloud) over five Adifferent ecosystems. Based on the results of individual tests run as part of this cloud Amask, an algorithm was developed to estimate the phase of the clouds (liquid water, ice, Aor undetermined phase). Finally, the cloud optical thickness and effective radius were Aderived for both water and ice clouds that were detected during one flight line on 4 June. AThis analysis shows that the cloud mask developed for operational use on MODIS, and tested Ausing MAS data in Alaska, is quite capable of distinguishing clouds from bright sea ice Asurfaces during daytime conditions in the high Arctic. Results of individual tests, Ahowever, make it difficult to distinguish ice clouds over snow and sea ice surfaces, so Aadditional tests were added to enhance the confidence in the thermodynamic phase of clouds Aover the Chukchi Sea. The cloud optical thickness and effective radius retrievals used Athree distinct bands of the MAS, with a recently developed 1.62- and 2.13-(mu)m-band Aalgorithm being used quite successfully over snow and sea ice surfaces. These results are Acontrasted with a MODIS-based algorithm that relies on spectral reflectance at 0.87 and 2.13 (mu)m.