The purpose of this model is to provide timely ocean wind observations. ASCAT wind data can act as a source of truth for what the actual wind was at a location and time on the ocean.

There is a tutorial available which presents a lot of information which will be useful to understand when using these models.

• ASCAT tutorial

LuckGrib provides the ASCAT data in two separate models:

• ASCAT Latest (most recent 12 hrs.)
• ASCAT Orbits (2 days of data.)

This page describes the second model above, the Orbits model.

The ‘ASCAT Orbits’ model

During the development of this version of the ASCAT model, one of the first experiments on how to package it was to present single orbits of data in the GRIB file, with the two satellites each in their own record. This presentation ended up being quite difficult to use in practice.

After a series of experiments, the final form for this model was chosen:

Each GRIB record contains 6 hours of data.

There are four GRIB records created for each day, each containing approximately 6 hours of wind observation data. As the main purpose of this model is for the validation of forecast data at the synoptic times, the GRIB records created contain wind observation data which is centered on each synoptic time. Each GRIB record contains 6 hours of ascending and descending wind observations, from the metop-b and metop-c satellites.

GRIB @ 06Z:       03Z +++ 09Z
GRIB @ 12Z:            |  09Z +++ 15Z
GRIB @ 18Z:            |       |  15Z +++ 21Z
GRIB @ 00Z:            |       |       |  21Z +++ 03Z
                       |       |       |       |
hours:       00Z  03Z 06Z 09Z 12Z 15Z 18Z 21Z 00Z 03Z ...

For example, a GRIB record with a 12Z reference time, the second line above, will contain data from 09Z through to 15Z. This makes the 12Z ASCAT data ideal for validating 12Z forecast data.

Of course, there may not be ASCAT wind data available in your area of interest at the forecast time, but you can start there and then search to find the freshest data for your location.

Timeliness of the data.

The ASCAT model on the LuckGrib server updates frequently, but on a somewhat irregular schedule, ranging from 40 minutes to a little over an hour. The updates occur quickly after the satellite data provided by NASA becomes available.

When there is new satellite data available, LuckGrib downloads its content and processes the most recent (approx) two days of data into a fresh model run.

If you use download ASCAT data using this model, for a large area, frequently, over the period of 6 to 12 hours, you will see the final GRIB record slowly accumulate more and more orbit data.

Update reliability

Please read the Note on reliability in the tutorial. This data is considered non-operational and from time to time updates can be delayed, for up to several days at a time. Data is updated on a best effort basis.