REMOTE MEASUREMENT OF SURFACE TEMPERATURE AND ITS APPLICATION TO ENERGY BALANCE AND EVAPORATION STUDIES OF BARE SOIL SURFACES.
AGRICULTURAL RESEARCH SERVICE TEMPE ARIZ WATER CONSERVATION LAB
Pagination or Media Count:
The report deals with the measurement of surface temperature under field conditions using an infrared radiometer with a bandpass of 600 to 1300cm 16 - 7.5 microns. The usefulness of such a method in measuring latent and sensible heat flux over a wet, bare soil surface is explored. A review is given of similar work reported by others and of available methods for using surface temperatures in flux calculations. The theory of infrared thermometry is extensively reviewed and the necessity of measuring surface emittance and sky radiance is explained. A description is given of experimental methods for the calibration of the radiation thermometer, the measurement of surface emittance and of sky radiance, the latter employing a standard surface of which the temperature is monitored. Also, an account is given of equipment and methods for routine measurement of surface temperatures in the field. On three days in the spring of 1966, a comparison was made of measured and calculated evaporation. The measurements were obtained with weighable lysimeters and the calculations based upon radiometrically obtained surface temperatures. The agreement was excellent, proving the adequacy of the log-law transfer function relating vapor gradient to vapor flux. This function can be stated simply as the product of windspeed and drag coefficient. A comparison of similarly computed sensible heat flux with residual values for the same quantity obtained from the energy balance proved inconclusive. This result is attributed mainly to the incidence of vertical divergence of sensible heat flux and to the inequality of transfer coefficients for momentum and sensible heat. Author
- Agricultural Engineering