Comparison of NASA Icing Remote Sensing System and Balloonsonde Measurements at AIRS II

As part of the NASA aircraft icing program, atmospheric remote sensing technologies are being developed with the goal of providing flight crews with adequate warning to avoid regions of potential danger. A suite of instruments including radar and microwave radiometry is used to identify a region of supercooled liquid water which is labeled as hazardous if its water content is sufficiently high. A balloonsonde system is employed to provide in-situ measurement of the atmospheric conditions against which the remote sensing results can be compared. Among the parameters compared are cloud upper and lower boundaries, temperature and humidity profiles, and freezing levels. These instruments were deployed at the Alliance Icing Research Study (AIRS II) near Montreal, Quebec during the winter of 2003 – 2004. A total of 89 balloonsonde launches took place during the field study, 70 of them during the period of time that the NASA icing remote sensing instruments were on-site. Initial comparisons from a limited number of cases showed that with regards to temperature, agreement was good between the balloonsonde and the remote sensing instruments, particularly at altitudes below 6 kilometers. With regards to relative humidity, larger discrepancies are seen, especially when rapid changes in humidity are encountered or when the relative humidity is low (<40%). In this paper, the processed data from the NASA remote sensing instruments will be compared in detail with the soundings from the balloonsonde system for those cases where both remote sensing and balloonsonde data are available.