抄録
A method to estimate semitransparent cirrus height together with temperature from the observed data of the water vapor absorption channel (Chan. 2 : 6.0-7.0um) and window channel (Chan. 3 : 10.5-11.5 um) of VTIR (Visible and Thermal IR Radiometer) onboard MOS (Marine Observation Satellite)-1 is developed.
The method is based on the radiative transfer model. In the derivation of the estimating formula following assumptions are made. (1) Scattering effect in the cirrus is neglegibly small in the spectra of these channels. (2) The temperature of cirrus and lower boundary (sea surface) is homogeneous in the area for computation. (3) The emissivity of the cirrus is equal in these spectra. (4) The temperature of the cirrus is equal to that of the ambient air.
Under the above assumptions, radiance of Channel 2 (R 2) can be expressed in terms of the radiance of Channel 3 (R 3) as follows.
R 2=aR 3+b, where a and b are determined through the least square method. Then the height of the cirrus can be decided through following procedures. (1) Compute radiances from the cirrus at the height of the initial guess for Channels 2 and 3. (2) Substitute the computed R 2 and R 3 into the above equation. If the equality doesn't hold adjust the initial guess height of the cirrus and repeat the procedure until the equality is reached. The height where the equality is satisfied is the cirrus height and the air temperature of that height is the cirrus temperature.
In the computation of the radiative transfer equation, the upper air data provided by the numerical weather prodiction group can be utilized.
Results of verifications indicates that there is a good correspondence between the height of cirrus estimated based on the proposed method and that obtained from the data of radiosoundings.
