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Since 1998 the Southampton Oceanography Centre (SOC),
in collaboration with Brookhaven National Laboraties (BNL),
the European Joint Research Centre (JRC),
and the Met Office, has been engaged in
various instrument development activities with the objective of delivering autonomous,
ship-based in situ skin sea surface temperature (SST) measurements in an operational
manner to validate skin SST. The result of these efforts is the Infra-red SST
Autonomous Radiometer (ISAR) which can be deployed on ships of opportunity unattended
for periods of up to six months with a SST measurement accuracy of ± 0.1K.
ISAR and optical rain gauge onboard the Pride of Bilbao
The ISAR instrument measures in the spectral waveband of 9.8 - 11 &mu m and has a
measurement range from 173 - 373 K. The onboard calibration is done by
two radiance cavities, one heated and one at ambient temperature. The infrared radiation
is reflected via a 45° mirror on scan drum through a water proof window onto the infra-red
sensor. A scan drum cycle includes the two radiance cavities, a sea view, an
atmospheric view and a sky view and can be completed once per minute.
The ISAR also incorporates a roll and pitch sensor to validate the measurement angles
and a GPS for position information. Furthermore it has a shutter mechanism which
closes when rain or spray is detected by the optical rain gauge, thus protecting the
instrument from water ingress on the critical optical surfaces.
Three shutter postions of the ISAR; in the left image the shutter is open
and the mirror is looking towards the atmosphere,
in the middle image the shutter is open and the mirror is looking
into the calibration cavity and in the right image the shutter is closed.
To improve the quality of the skin SST measurement a number of ancillary instruments
can be connected to the ISAR, where the data is logged. The instruments which are
currently used on deployments such as on the Pride of Bilbao are a hull mounted
thermometer a pyranometer and a anemometer.
The Pride of Bilbao with the Instrument positions labelled.
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