Estimation of Cirrus and Stratus Cloud Heights Using Landsat Imagery

摘要

A new method based upon high-spatial-resolution imagery is presented that matches cloud and shadow regions to estimate cirrus and stratus cloud heights. The distance between the cloud and the matching shadow pattern is accomplished using the 2D cross-correlation function from which the cloud height is derived. The distance between the matching cloud-shadow patterns is verified manually. The derived heights also are validated through comparison with a temperature-based retrieval of cloud height. It isalso demonstrated that an estimate of cloud thickness can be retrieved if both the sunside and antisunside of the cloud-shadow pair are apparent. The technique requires some intepretation to determine the cloud height level retrieved (i.e., the top. base, or mid-level). It is concluded that the method is accurate to within several pixels, equivalent to cloud height variations of about ±250 m. The results show that precise placement of the templates is unnecessary, so that the development of a semiautomated procedure is possible. Cloud templates of about 64 pixels on a side or larger produce consistent results. The procedure was repeated for imagery degraded to simulate lower spatial resolutions. The results suggest that spatial resolution of 159-200m or better is necessary in order to obtain stable cloud height retrievals.