imaging Satellite Humidity And Instability product
Operationally produced by NWC SAF.
To provide an estimation of precipitable water (in total column and in three layers), stability indices, total ozone and skin temperature.
✓ iSHAI is available during both day and night-time.
✓ iSHAI can be generated for every new satellite image (every 15 minutes; 5 minutes in the case of Rapid-Scan).
✓ iSHAI product is generated locally by the users executing the GEO-iSHAI program. This allows use of local NWP model as the NWP background.
X Not available on cloudy pixels. Once the clouds develop only information from neighborhood is available.
X The iSHAI product is generated on boxes of N x N pixels (where N is configurable by the users). The size of the default box is 3×3; but can be generated in 1×1. The execution time of iSHAI could be huge for large regions if processed with N too low.
X Droplet/crystal size, Cloud optical thickness, Liquid and Ice water path are not retrieved at nighttime and in case mixed/undefined phase or too thin clouds.
X The cloud mask near edge of clouds tends to produce larger differences with the background NWP perhaps due to cloud contaminated pixels.
X MSG satellites have few IR and WV channels: not enough information to modify the background NWP profile.
X The main errors are related to disagreement between the background NWP model used and the true atmosphere. It is recommended to use profiles with as much spatial, temporal and vertical resolution as possible.
Accessibility and Dissemination:
- Local installation: Product is accessible after registration (signed contract) at NWCSAF and installation of NWCSAF GEO V2016 in the local environment. It can be run every 15 minutes or with the different settings every 5 minutes RSS. Output format is NetCdf.
- Images for the last 24h, updated every 15 minutes at NWCSAF web site: http://www.nwcsaf.org/ishai_sai
Overview modified after NWC SAF Practical Guide by V. Nietosvaara, EUMETSAT, 2018.