8
digitally storable readouts. More elaborate active measurement instruments require
probes to be applied to the target necessitating an acoustic, electrical, or electromagnetic source and associated circuitry for conditioning of the probe signal.
Well calibrated, many of these variables can be reported on the scales of the
International System for Weights and Measures (SI for the French Système international d’unités) which govern these fundamental measurements assuring widespread consensus on data accuracy and precision (Bureau International des Poids et
Mesures 2006).
An exponential increase in capability of underwater instrumentation has been
fueled by the advent of modern electronics. Electronic signal detection and amplification technology was originally developed for radio communications and artillery
ranging and detection during the Second World War. Vacuum cathode ray devices
that amplify and modulate electronic signals permitted sending and receiving atmospheric radio signals and, subsequently, underwater acoustic signals. Modern
devices incorporating solid state technology far surpass the performance and reliability of the original vacuum tube and have allowed miniaturization of the components and freedom from the fragile, failure prone vacuum tube technology of
50 years ago. Solid state transistors, at the heart of all electronic instruments today,
are composed of semiconductor mineral phases of materials such as silicon and
germanium. Diodes (bipolar transistors) consist of a monolithic physical junctions
of two such mineral formulations displaying opposite negative (N) or positive (P)
electronic properties. Electrical leads to the source (positive) and from the drain
(negative) connect the device to the operating circuit. Diodes permit current flow in
only one direction, constituting effective electronic on/off valves that rectify oscillatory alternating current to flow in only one direction. Signal amplification transistors known as bipolar junction transistors incorporated an additional mineral phase
gate interposed between the diode elements yielding the configurations PNP or
NPN. These electronic valves, analogous to the triode vacuum tubes of (recent)
yore, allow amplification of the low power signal through modulation imparted to a
carrier wave. The low power signal energizes the central gate element in a pattern
dictated by the sensor and transmitted across the assembly to the drain element both
as amplified by the source and as modulated by the gate. Such power transistors are
recognizable in electronic circuits as those attached to large fluted metal heat sinks.
Power transistor heat loss however constitutes a limiting factor for the operation of
remote sensors. In practice, these transistors are incorporated into integrated amplification circuits such as the well-known analog operational amplifier. External oscillator circuits feeding op/amps provide frequency modulation. Since the signal from
any electronic transducer including acoustic, radio, microwave, and optical emission may be similarly modulated, the application of solid state technology using
electronic sensors is extended to many practical ocean observing applications here
discussed. In addition to primary data sensing, separate circuitry is required for
electronic data conditioning and transmission (Chap. 5).
Today diode- and triode-like logic gate transistors in integrated circuits (IC) with
dimensions down to 45 nm can have transistor counts of more than 10
9
per IC. The
metal oxide semiconductor field effect transistor (MOSFET) and similar designs have
proved especially suitable for incorporation into these circuits that are fabricated
2 Electronic Sensors and Instruments for Coastal Ocean Observing
digitally storable readouts. More elaborate active measurement instruments require
probes to be applied to the target necessitating an acoustic, electrical, or electromagnetic source and associated circuitry for conditioning of the probe signal.
Well calibrated, many of these variables can be reported on the scales of the
International System for Weights and Measures (SI for the French Système international d’unités) which govern these fundamental measurements assuring widespread consensus on data accuracy and precision (Bureau International des Poids et
Mesures 2006).
An exponential increase in capability of underwater instrumentation has been
fueled by the advent of modern electronics. Electronic signal detection and amplification technology was originally developed for radio communications and artillery
ranging and detection during the Second World War. Vacuum cathode ray devices
that amplify and modulate electronic signals permitted sending and receiving atmospheric radio signals and, subsequently, underwater acoustic signals. Modern
devices incorporating solid state technology far surpass the performance and reliability of the original vacuum tube and have allowed miniaturization of the components and freedom from the fragile, failure prone vacuum tube technology of
50 years ago. Solid state transistors, at the heart of all electronic instruments today,
are composed of semiconductor mineral phases of materials such as silicon and
germanium. Diodes (bipolar transistors) consist of a monolithic physical junctions
of two such mineral formulations displaying opposite negative (N) or positive (P)
electronic properties. Electrical leads to the source (positive) and from the drain
(negative) connect the device to the operating circuit. Diodes permit current flow in
only one direction, constituting effective electronic on/off valves that rectify oscillatory alternating current to flow in only one direction. Signal amplification transistors known as bipolar junction transistors incorporated an additional mineral phase
gate interposed between the diode elements yielding the configurations PNP or
NPN. These electronic valves, analogous to the triode vacuum tubes of (recent)
yore, allow amplification of the low power signal through modulation imparted to a
carrier wave. The low power signal energizes the central gate element in a pattern
dictated by the sensor and transmitted across the assembly to the drain element both
as amplified by the source and as modulated by the gate. Such power transistors are
recognizable in electronic circuits as those attached to large fluted metal heat sinks.
Power transistor heat loss however constitutes a limiting factor for the operation of
remote sensors. In practice, these transistors are incorporated into integrated amplification circuits such as the well-known analog operational amplifier. External oscillator circuits feeding op/amps provide frequency modulation. Since the signal from
any electronic transducer including acoustic, radio, microwave, and optical emission may be similarly modulated, the application of solid state technology using
electronic sensors is extended to many practical ocean observing applications here
discussed. In addition to primary data sensing, separate circuitry is required for
electronic data conditioning and transmission (Chap. 5).
Today diode- and triode-like logic gate transistors in integrated circuits (IC) with
dimensions down to 45 nm can have transistor counts of more than 10
9
per IC. The
metal oxide semiconductor field effect transistor (MOSFET) and similar designs have
proved especially suitable for incorporation into these circuits that are fabricated
2 Electronic Sensors and Instruments for Coastal Ocean Observing