Cloud Top Temperature and Height (CTTH)
Contents:
Goal of the ctth product
The output provides information on the temperature and height/pressure (in meters or Pa) of opaque, semi-transparent and sub-pixel cloud tops.
The main use of this product is in the analysis and early warning of thunderstorm development and the height assignment for aviation forecasting. The product may also serve as input to mesoscale models for use in Nowcasting in general, or as input to other satellite retrievals used for Nowcasting. The nwcsaf/pps ctth retrieval, based on imager data from polar orbiter, will also be used to build up cloud climatologies within the cmsaf.
ctth algorithm summary
The ctth will take as input the Cloud Mask. Mandatory spectral information is an 11 micron channel and additionally a 3.7 or 12 micron channel. The optional channels 6.7, 7.3, 8.5 or 13.3 microns may improve the results. The CTTH further requires NWP short range forecast data in high vertical resolution. The cloud top pressure is derived using neural network. This means that an artificial neural network has been trained (i.e. the cost-function has been minimized for a dataset of given input and output data) carefully offline. The derived system of weights and functions is then applied to actual input data which give direct output on the same spatial resolution. For a more detailed overview about the training and application processes, please refer to the according ATBD.
The ctth output
The CTTH output consists of:
- Three parameters for the cloud top main output: Temperature, Pressure and Height
- Three quality/conditions flags
Main output
The ctth produces three parameters for the cloud top:
- Temperature in Kelvin
- Height in meters
- Pressure in Pa