High-Resolution Image

The NASA TC4 (Tropical Composition, Cloud and Climate Coupling) mission was designed to investigate the structure, properties and processes in the tropical Eastern Pacific. The mission involved the coordination of high and medium altitude aircraft and satellite observations to provide crucial information on the spatial and temporal variations of this region.

Among several instruments onboard the high altitude NASA ER-2 aircraft is the MODIS Airborne Simulator (MAS). MAS is a 50 channel airborne scanning spectrometer (0.47 to 14.2 µm) that acquires high spatial resolution imagery of cloud and surface features. In TC4 MAS was employed to determine cloud property information: in particular cloud thermodynamic phase, optical thickness and effective particle radius.

A three-panel sample of MAS cloud property information acquired from 1443 to 1449 GMT on July 17, 2007 over the eastern Pacific is provided. The leftmost panel is an RGB image of 3 MAS bands (2.13 µm, 1.6 µm and 0.65 µm), the middle panel cloud optical thickness (tau), and the rightmost panel cloud effective particle radius (re). In the RGB image, high clouds (ice) tend to be blue to violet and water clouds yellowish. In the upper and lower parts of the imagery, high clouds (cirrus anvils) are prominent, with water cloud and some cirrus apparent towards the middle parts of the image. To interpret the tau and re imagery, the images are based on a dual color bar scale where the cold colors (greens to violet) are data identified as ice cloud and the warm colors (yellows to reds) as water cloud.

All MAS pixels in this scene have been identified by the retrieval algorithm as being cloud and with a phase of ice, water, or undetermined (processed as water). Virtually all pixels successfully return an optical thickness value (though the low “yellow” values near the top of the image are suspect due to cloud shadows). The effective radius imagery shows successful retrievals for the thicker ice cloud regions with some problems in the central parts of the image where the cirrus is thinner and the lower water cloud is more apparent. These “multi-layer” clouds (thin cirrus over water cloud) are the subject of much current research as to how to get a successful effective radius retrieval.

Of interest as well in this scene is the narrow vertical cloud line that is apparent near the middle of each image. This cloud is actually the contrail of the NASA DC-8 aircraft flying in coordination with the ER-2; solid evidence that the aircraft coordination was quite good at this time. Good aircraft coordination is a critical component to validating the ER-2 and satellite remote sensing measurements. (Submitted by G. T. Arnold, M. D. King, S. Platnick, and G. Wind.)