ASCAT L3 — Scatterometer Observations

What This Dataset Is

ASCAT Level-3 (L3) winds are derived directly from measurements made by the ASCAT scatterometer instruments onboard the MetOp satellites. These instruments measure radar backscatter from the ocean surface, which is related to surface roughness and therefore wind speed and direction.

L3 products are gridded versions of individual satellite overpasses. They represent real satellite observations aggregated onto a regular latitude/longitude grid.

How It Works

1. The satellite passes over the ocean and measures microwave backscatter.
2. A geophysical model function converts backscatter into wind speed and direction.
3. Observations are quality-controlled.
4. Valid winds are gridded to a fixed spatial resolution (e.g., 0.25°).
5. No large-scale interpolation is applied — if the satellite did not observe a location, it remains empty.

Strengths

• Directly observation-based
• No large-scale model interpolation
• Preserves sharp gradients and wind transitions
• Represents true measurement frequency
• Scientifically transparent

Limitations

• Incomplete spatial coverage (swath gaps)
• Limited local-time sampling (orbit-dependent)
• Directional sampling bias possible
• Rain and quality filtering can remove valid winds
• Sparse coverage can exaggerate “zero” directions in wind roses

Appropriate Uses

• Observational climatology
• Satellite-based wind frequency analysis
• Research requiring measurement authenticity
• Applications where gaps are acceptable

Not Recommended For

• Navigation planning
• Safety-critical operations
• Real-time decision-making
• Complete spatial coverage requirements