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Ocean Surface Topography from Space


OSTM/Jason-2   Radiometer
The Advanced Microwave Radiometer (AMR), is an enhanced version of the Jason-1 Microwave Radiometer (JMR). Like the JMR, it acquires measurements via three separate frequency channels (23.8, 18.7 and 34 GHz) to determine the path delay of the altimeter's radar caused by atmospheric water vapor. Measurements acquired at each frequency are combined to determine atmospheric water vapor and liquid water content. Once the water content is known, the correction to be applied for radar signal path delays can be determined.

Additional information on the AMR is available on the AVISO site.


Jason-1 Radiometer
The JMR, Jason Microwave Radiometer, acquires measurements via three separate frequency channels to determine the path delay of the altimeter's radar signal due to atmospheric water vapor. Its measurements can also be used directly for studying other atmospheric phenomena, particularly rain.

To determine atmospheric water vapor content accurately, we need to eliminate sea surface and cloud contributions from the signal received by the radiometer. That is why the JMR uses three different frequencies:

  • Redundant 23.8GHz channel measures atmospheric water vapor emission
  • 18.7 GHz Channel correct for ocean surface effects
  • 34.0 GHz Channel corrects for non raining clouds

By combining measurements acquired at each of these frequencies, we can extract the water vapor signal.

Additional information on the JMR is available on the AVISO site.


TOPEX/Poseidon   Radiometer
The TOPEX/Poseidon microwave radiometer was a three-frequency sensor used to estimate the atmospheric water vapor content in the nadir column through which the altimeter signal is traveling. Since water vapor distorts the altimeter's reading, the water vapor content is measured to correct the altimetry measurement. The sensor uses one frequency to make the measurement, and two frequencies to remove the effects of wind speed and cloud cover. There is a backup receiver for the measurement frequency.

Additional information on the TMR is available on the AVISO site.

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