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A picture of a DWR-MkIII, a DWR-G and a DWR4.

Compact Air Temperature (CAT4) antenna

An accurate and reliable air temperature measurement at sea is quite a challenge. On the one hand, compared to a land-based sensor, spray and reflection of the solar radiation on the water surface pose extra requirements on the shielding of the temperature sensor, while on the other hand the marine environment is notoriously hard for mechanical constructions.

A picture of a CAT4 antenna with a background of the sea
A Compact Air Temperature (CAT4) antenna on a DWR4 /ACM.

Therefore, the shielding of a temperature sensor on a small buoy becomes a trade-off between functionality and vulnerability. An innovative design developed by Datawell for integration into our Waverider buoys, senses the impact of radiation and evaporation instead of shielding the temperature sensor. This highly effective design avoids the trade-off altogether, all while maintaining the HF communication functionality.

By now, this novel design has been proven in multiple real world applications. Based on three temperature measurements which are influenced in different manners by external factors, the air temperature can be calculated. A fourth sensor allows for determining if the antenna is wet, in which case the measurement is flagged.


The flashlight ensures good visibility of the instrument.

Black shield

The black colour of the shield around this sensor makes it heat up by solar radiation significantly more than the other sensors do.

White shield

The white shield, which is made of the same material as the black shield, heats up less than the black shielded sensor. Hence, influences of solar radiation can be determined and compensated for.

Metal shield

The metal shielded sensor differs significantly in infrared emissivity from the former two sensors, which are made of a plastic.

Grooved shield

A grooved shield holds more water than the other shields do. Being the sensor closest to the sea surface allows to check if evaporation of water is occurring.