Optical thickness and effective radius of Arctic boundary-layer clouds retrieved from airborne nadir and imaging spectrometry

[摘要] Arctic boundary-layer clouds in the vicinity of Svalbard (78° N,15° E) were observed with airborne remote sensing and in situmethods. The cloud optical thickness and the droplet effective radius areretrieved from spectral radiance data from the nadir spot (1.5°,350–2100 nm) and from a nadir-centred image (40°, 400–1000 nm).Two approaches are used for the nadir retrieval, combining the signal fromeither two or five wavelengths. Two wavelengths are found to be sufficientfor an accurate retrieval of the cloud optical thickness, while the retrievalof droplet effective radius is more sensitive to the number of wavelengths.Even with the comparison to in-situ data, it is not possible to definitelyanswer the question which method is better. This is due to unavoidable timedelays between the in-situ measurements and the remote-sensing observations,and to the scarcity of vertical in-situ profiles within the cloud.

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