We present updated zonal wind measurements of Saturn using Cassini ISS images taken between 2004 and 2014. We previously reported that there may be small seasonal changes in Saturn’s zonal wind profile but measurement uncertainties prevented us from making definite statements. In our previous report, we used the zonal standard deviation of the wind vectors as a proxy for the measurement uncertainty. However, zonal standard deviation contains contributions from both real spatial variations in the wind speed as well as uncertainties in the measurements. This raised a difficulty in distinguishing small, real changes in the wind field from the uncertainties in the measurement. We have developed a technique which isolates real spatial variations from measurement uncertainties by analyzing the correlation fields produced in the two-dimensional Correlation Imaging Velocimetry (CIV) cloud-tracking wind measurement method. The CIV algorithm computes a wind vector by calculating the two-dimensional correlation between the pair of maps; a peak in the correlation is judged to be a match. We determine the size, shape, and orientation of the peak by fitting an ellipse to the peak and calculating the area, eccentricity, and orientation angle of the ellipse. Combining these metrics provides a measure of the uncertainty associated with individual wind vectors. Vectors with smaller, sharper, more circular peaks will have a smaller uncertainty than vectors with larger, flatter, more elliptical peaks. Using this new technique, our new measurements reveal small temporal changes in the zonal wind profiles. Our work has been supported by NASA PATM NNX14AK07G and NSF AAG 1212216.
AAS/Division for Planetary Sciences Meeting Abstracts #47
- Pub Date:
- November 2015