Measurement of Radiation Losses Over Thermal Ground Using a Calorimeter

Abstract

The total (q tot) and convective (q conv) fluxes at the surface of thermal ground can be measured with a ground calorimeter. The difference (q tot – q conv) at a given site equals the subsurface conductive flux (q cond) which at the surface splits into a surface conductive (q0 cond) and a radiation (q rad) component. The anomalous radiation flux (
q rad), with respect to ambient temperature, can be assessed by separating the meter from the ground using a small air gap. Measurements over the Karapiti steaming ground field (Wairakei, NZ) have shown that the ratio (
q rad / q tot) is independent of (q tot). The measurements at 15 sites point to a ratio (
q rad / q tot) of 0.22 +/- 0.06 which implies that at least c. 1/5 of the total flux is transferred from thermal ground to the calorimeter by radiation. The ratio is slightly larger if the IR reflectance of the calorimeter bottom (about 0.2) is considered.