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Mapping Heat Flux

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  • 1 Naval Research Laboratory, Oceanography Division, Remote Sensing Applications, Stennis Space Center, Mississippi
  • | 2 Naval Research Laboratory, Washington, D.C.
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Abstract

An infrared camera technique designed for remote sensing of air–water heat flux has been developed. The technique uses the differential absorption of water between 3.817 and 4.514 microns. This difference causes each channel’s radiance to originate over a different range of depths inside the air–water interface temperature gradient. Since this gradient varies only with total heat flux, the radiance difference between channels caused by the gradient also varies with heat flux. Laboratory experiments showed that this radiance difference correlates well with heat flux measured independently with calorimetry. A regression relation between camera output and heat flux is determined initially using time variations of the radiance difference and heat flux. This relation is modified by a partial differential analysis of the relative contributions of temperature and heat flux using data from experiments designed for this evaluation. The result is applied to the spatial variations of radiance difference in a single image pair. Error is controlled in this sensitive measurement with narrowband filters, a low-noise infrared camera, and frame averaging. Averaging all image pixels reduces modeled and measured error to rmse Q ≅ 3.1 W m−2.

Corresponding author address: Mr. Walt McKeown, Oceanography Division, RSA, Code 7340, Naval Research Laboratory, Stennis Space Center, MS 39529-5004.

Email: waltm@ltm.nrl.navy.mil

Abstract

An infrared camera technique designed for remote sensing of air–water heat flux has been developed. The technique uses the differential absorption of water between 3.817 and 4.514 microns. This difference causes each channel’s radiance to originate over a different range of depths inside the air–water interface temperature gradient. Since this gradient varies only with total heat flux, the radiance difference between channels caused by the gradient also varies with heat flux. Laboratory experiments showed that this radiance difference correlates well with heat flux measured independently with calorimetry. A regression relation between camera output and heat flux is determined initially using time variations of the radiance difference and heat flux. This relation is modified by a partial differential analysis of the relative contributions of temperature and heat flux using data from experiments designed for this evaluation. The result is applied to the spatial variations of radiance difference in a single image pair. Error is controlled in this sensitive measurement with narrowband filters, a low-noise infrared camera, and frame averaging. Averaging all image pixels reduces modeled and measured error to rmse Q ≅ 3.1 W m−2.

Corresponding author address: Mr. Walt McKeown, Oceanography Division, RSA, Code 7340, Naval Research Laboratory, Stennis Space Center, MS 39529-5004.

Email: waltm@ltm.nrl.navy.mil

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