Optimal Cloud Analysis (OCA)
Demonstrational product by EUMETSAT.
Optimal Cloud Analysis provides cloud microphysical and bulk properties from the MSG SEVIRI instrument. Basic parameters provided are:
• Phase (ice/liquid/Multi-layer)
• Optical Depth
• Effective Radius
• Top pressure
In the Multi-layer case parameters are provided for upper (assumed ice phase) and lower (assumed liquid phase) layers. Currently effective radius is not available for the lower layer.
With all parameters there is an associated error estimate and an overall quality measure indicates the confidence in the retrieval (per pixel).
The product can be used in applications requiring cloud properties from medium spatial resolution (3-~6 km) and high temporal resolution (15 minutes): Nowcasting, model verification, precipitation estimation (as a derived product), etc.
✓ Availability 3 km @Sub-Satellite-Point every 15 minutes.
✓ Two-layer capability (most other products limit to a single layer).
✓ Error estimates.
✓ Permits overshooting tops (some other products limit to tropopause).
X Nighttime product inferior to daytime as all channels used in solar illumination.
X Multi-layer conditions only detected for moderate cirrus optical depths (<~4-5).
X Complex compared to single layer analogues – attention to error estimates!
OCA Product slide-show.
Accessibility and Dissemination:
Peer Review Journal Papers:
Poulsen, C. A., P. D. Watts, G. E. Thomas, A. M. Sayer, R. Siddans, R. G. Grainger, B. N. Lawrence, E. Campmany, S. M. Dean, and C. Arnold
(2011), Cloud retrievals from satellite data using optimal estimation: Evaluation and application to ATSR, Atmos. Meas. Tech. Discuss., 4,
Extension to 2 layers (OCA):
Watts, P. D., R. Bennartz, and F. Fell (2011), Retrieval of two‐layer cloud properties from multispectral observations
using optimal estimation, J. Geophys. Res., 116, D16203, doi:10.1029/2011JD015883.
Overview by Phil Watts, EUMETSAT, 2018.