4.2 Long wave radiation
Downward and upward long wave radiation was
calculated from the empirical models.
4.2.1 Downward long wave radiation:
Downward long wave radiation (D) was calculated from
the following empirical model.
L = oT*{0.61-0.058 le} ....(9)
where T: temperature (K^), e: vapor pressure (mmHg).
Vapor pressure e is computed using the equation:
ezew(t)-CpP/0.6221(t-t) ...... (10)
where e: vapor pressure (mb), Cp: specific heat of air at
constant pressure, P: air pressure, 1: 580 cal/g, t;' t:
temperature of wet and dry thermocouple thermometers, .
ew: saturated vapor pressure.
In remote sensing, difficulties with the measurement of
wet-bulb temperature make it necessary to assume that
both wet and dry bulb thermometers' temperatures are
equal. Therefore, we applied the above Seino and
Uchijima vapor pressure model based on data for a
humid climate. Similar vapor pressure models are
expected to develop for application in regions with
different climates.
Figure 12 shows daytime downward long wave radiation
in the Hokkaido Island, Japan.
4.2.2 Upward long wave radiation: Upward long
wave radiation is estimated by the following equation:
U- 8o(1Is4 273.8) 4 (1,8) L 2 (11)
where à: emissivity, ©: Stefan Boltzmann constant,
Ts: surface temperature (C^), L: downward long wave
radiation
Figure 13 shows daytime upward long wave radiation in
the Hokkaido Island, Japan.
4.2.3 Effective radiation: Then, effective
radiation (F) is calculated using the following equation:
F=L-U ....(12)
where F:effective radiation, L: downward longwave
radiation, U: upward longwave radiation.
4.3 Net radiation
Net radiation (S) is obtained by the following;
S. (Cnm ) RocR renes (13)
where S: net radiation, a": albedo (estimated albedo in
each pixel), R: downward short-wave radiation, F:
effective radiation. :
Each net radiation during the day and at night was
calculated by this process, and the amplitude of net
radiation dS was obtained by subtracting net radiation at
night from that during the day.
Figure 14 shows daytime net radiation in the Hokkaido
Island, Japan.
888
Fig. 12 Distribution of downward longwave
radiation in and around Hokkaido
Island, Japan (Oct. 17, 1990).
Fig. 13 Distribution of upward longwave
radiation in and around Hokkaido
Island, Japan (Oct. 17, 1990).
Fig. 14 Distribution of net radiation in and
around Hokkaido Island, Japan (Oct.
17,1990).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
QA e p o5 . 7
ve
ga