Aircraft measurements of the albedo of the earth's surface and of clouds over India

Abstract

Measurements of global and reflected solar radiation and of the earth's albedo over extensive land areas in India and over the adjoining seas were made from a Canberra aircraft during July-August 1972 as part of an Indo- U .K. Project Exercise Storm Exchange. Two thermoelectric pyranometers, one facing upwards and the other facing downwards, were used to measure the global and reflected solar radiation, a photographic recorder with suspended coil mirror galvanometers recording the data continuously in flight.

Twenty aircraft flights were made from three bases, 7 from Bangalore, 8 from Poona and 5 from Calcutta, over both land and sea, covering areas from 7°N to 24⁰N and 71°E to 89°E. The aircraft flew at heights above ground/ sea  from 150 to 15,000m.

The values of global solar radiation recorded were of the order of J. 60 to 1.80 cal/cm²/min at heights of 4,600 m to 15,000 m, when there were no clouds; thin cirrus reduced this value by about 16 to 20 per cent and other clouds by larger amounts depending on their type and thickness.

The albedo over the sea was found to vary between 0.04 to 0.13, depending on the state of the solar elevation and that over the ground between 0.10 to 0.25. The albedo over active cumulus clouds was about I 0'40 to 0.60 and that over cumulus of smaller extent between 0.25 and 0.40. Stratocumulus clouds have smaller albedo 0.20-0.40 and stratus, 015-0.25. The albedo of altostratus clouds was found to lie between 0.25 and 0.35. The albedo of the cirrus remains of dissipating cumulonimbus clouds was about 0.45 to 0.55. In the growing cumulus cloud the albedo changes from 0.20 to 0.55 depending on the stage of growth. Albedo values change from 0.16-0.27 to 0.30-0.36, when stratus and stratocumulus clouds are associated with cirriform clouds.

The observations are compared with satellite and ground observations of surface albedo over India.