11
and inverse, with greater resistance at lower temperatures. The pronounced nonlinearity necessitates rigorous calibration and data processing to achieve accurate
results throughout the temperature range. Since thermistors are more economical to
produce and can provide greater precision and temporal resolution, oceanographic
practice trends in this direction although in full recognition that the PRTD remains
the primary reference for temperature determination.
Modular electronic temperature sensing units are widely used and are available
in multiple application-targeted versions. High precision instruments using aged
glass coated thermistor beads calibrated in ITS-90-prescribed baths offer accuracy
to 0.001 °C and time responses down to 0.07 s. Electronic means also improve up to
tenfold over the accuracy of mercury thermometers. Yearly sensor drift of such
instruments can be as low as 0.002 °C. Wein Bridge oscillators, employing series
and parallel resistor and capacitor pairs (arranged in a diamond pattern reminiscent
of the legacy resistance-based Wheatstone Bridge) render frequency modulated data
allowing intrinsic frequency-keyed digitization of the sensor signal.
Satellite Radiometry
Remote sea-surface temperature measurements from aircraft or orbiting satellites
are achieved by means of pyrometers, remote sensing instruments designed to measure radiant heat flux taking advantage of thermal windows in the infrared and
microwave wavelength bands where absorption by atmospheric gases is minimal.
These space-borne instruments achieve sea surface pixel resolution on the order of
tens (in the best cases) to hundreds or thousands of meters. Microwave channels
exhibit poorer resolution than IR bands rendering their products (in the tens of km)
of marginal applicability to coastal ocean observing. Infrared instruments aboard
NOAA weather satellites have progressed from the high-resolution radiometer
(HRR) through the very high-resolution radiometer (VHRR) to the current thirdgeneration advanced VHRR (AVHRR) that afford surface resolution of 1.09 km.
Three IR bands (3.55–3.93, 10.30–11.30, and 11.50–12.50 μm) are used for night
cloud mapping and sea surface temperature determination.
Fig. 2.1 Platinum
resistance thermometer
integrated in a bulkhead
mounting as part of a CTD
package
2.2 Electronic Sensors and Instruments for Ocean Observing
and inverse, with greater resistance at lower temperatures. The pronounced nonlinearity necessitates rigorous calibration and data processing to achieve accurate
results throughout the temperature range. Since thermistors are more economical to
produce and can provide greater precision and temporal resolution, oceanographic
practice trends in this direction although in full recognition that the PRTD remains
the primary reference for temperature determination.
Modular electronic temperature sensing units are widely used and are available
in multiple application-targeted versions. High precision instruments using aged
glass coated thermistor beads calibrated in ITS-90-prescribed baths offer accuracy
to 0.001 °C and time responses down to 0.07 s. Electronic means also improve up to
tenfold over the accuracy of mercury thermometers. Yearly sensor drift of such
instruments can be as low as 0.002 °C. Wein Bridge oscillators, employing series
and parallel resistor and capacitor pairs (arranged in a diamond pattern reminiscent
of the legacy resistance-based Wheatstone Bridge) render frequency modulated data
allowing intrinsic frequency-keyed digitization of the sensor signal.
Satellite Radiometry
Remote sea-surface temperature measurements from aircraft or orbiting satellites
are achieved by means of pyrometers, remote sensing instruments designed to measure radiant heat flux taking advantage of thermal windows in the infrared and
microwave wavelength bands where absorption by atmospheric gases is minimal.
These space-borne instruments achieve sea surface pixel resolution on the order of
tens (in the best cases) to hundreds or thousands of meters. Microwave channels
exhibit poorer resolution than IR bands rendering their products (in the tens of km)
of marginal applicability to coastal ocean observing. Infrared instruments aboard
NOAA weather satellites have progressed from the high-resolution radiometer
(HRR) through the very high-resolution radiometer (VHRR) to the current thirdgeneration advanced VHRR (AVHRR) that afford surface resolution of 1.09 km.
Three IR bands (3.55–3.93, 10.30–11.30, and 11.50–12.50 μm) are used for night
cloud mapping and sea surface temperature determination.
Fig. 2.1 Platinum
resistance thermometer
integrated in a bulkhead
mounting as part of a CTD
package
2.2 Electronic Sensors and Instruments for Ocean Observing