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Empirical equations for
inter-conversion
Abstract
1. Introduction
2. Methods
2.1.1 Land-based TSR and PAR
in air
2.1.2 Solar elevation angles
2.1.3 Equations for computing
cloudiness
2.1.4 Conversion between TSR
and PAR
2.2.1 Air-water interface
measurements in distilled water
2.2.2 Air-water interface
measurements in Tampa Bay
2.2.3 Effects of waves on PAR
transmission through the air-water interface
2.3.1 PAR irradiance and
attenuation measurements in water of Tampa Bay
2.3.2 Laboratory measurements
of attenuation of water samples
2.3.3 Estimation of the ratio
of 4p
to 2p
PAR just below the air-water interface
2.3.4 Prediction of PAR in
water from land-based PAR
3. Results
3.1 Maximum TSR and PAR from
solar elevation angles
3.2 Conversions between types
of solar radiation in air
3.3 Transfer of radiation
across the air-water interface
3.3.1 Controlled measurements
of refraction in distilled water.
3.3.2 In-water extrapolation
of 2p
PAR to just below the air-water interface.
3.3.3 Controlled measurements
of effects of waves on 2p
PAR transmission through the air-water interface.
3.4 Conversion of 2p
and 4p
PAR just below the air-water interface.
3.5 Attenuation coefficients
3.5.1 Choosing attenuation
coefficients for water.
3.5.2 Comparison of diffuse
and scalar PAR attenuation coefficients measured
simultaneously.
3.6 Modeled results using
land-based PAR to predict PAR in water.
4. Discussion
Acknowledgements
References
Abstract
Empirical equations were developed for converting between total solar radiation and photosynthetically active radiation (PAR) and between 2p and 4p sensor geometries allowing one type of solar radiation data to be computed from another type. In situ and laboratory tests indicate that 2p PAR in air is a good estimator of 2p PAR in water just below a calm or rough water surface. Just below the water surface, 4p PAR was 1.29 times the 2p PAR. Land-based 2p PAR data (5-minute averages) were multiplied by 1.29 to convert to 4p PAR in water and observed attenuation coefficients were used to predict PAR at 3 depths. The predicted PAR values were compared to 10-second averages of 4p PAR measured in water. Using these concepts and land-based data from Tampa, 2p and 4p PAR just below the water surface of Tampa Bay is estimated at 1.1×1010 and 1.4×1010 micromoles of photons per square meter per year, respectively. Attenuation was measured simultaneously by 3 in situ methods and also by 2 laboratory methods.
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