Abstract
We have developed a model of radiation balance near ground level for application to satellite data. To apply the model to data, we measured air temperature, surface temperature, humidity and wind velocity every hour for 24 hours on concrete, asphalt, soil, grass and trees. In addition to these temporal measurements, we installed a station on the rooftop of Nara Women’s University for measurements of air temperature, surface temperature and humidity using a logger. We applied the model to ground measurement data. The model works well for concrete, asphalt, soil and grass. In addition to ground measurement data analysis, we have included some results of preliminary research using satellite data.

1. Introduction
Air temperature and surface temperature are important parameters for environmental studies and monitoring the energy cycle for land area. The ground surface exchanges energy with air as sensible heat or latent heat. Sensible heat is important especially for urban area environmental studies. The energy is directly transferred from heated surface to air and raised the air temperature. Latent heat is important expecially for vegetation area environmental studies. The energy is taken away by evaporation and the air temperature around the area is not raised.

Using satellite data, our ultimate objective is to make images of sensible heat flux latent heat flux and air temperature. The first aim of this study is to develop a model of radiation balance near ground level. Our second aim is to develop a method for applying the model to satellite data.

In this paper, we report the model of radiation balance near ground level and the results of research using satellite data.

2. A model of radiation balance near ground level
We considered the radiation balance on the ground and in an elementary slab of atmosphere of thickness dz at altitude z (Houghton, 1986). We simplify the situation by assuming 1) that there is no cloud,2 ) a plane parallel atmosphere uniform in the horizontal, 3) that the air density is uniform in the vertical near ground. We define the altitude z as from 0 (which is the ground to (which is the top of the atmosphere).


Figure1 : radiation balance near surface

2.1 The balance of radiation near the ground level
At first, we considered the balance of radiation near ground level. The incoming solar radiation at time t (S(t,0) (Wm-2)) plus the infrared radiation from the atmosphere at time t(F (t,0) (Wm-2)) directed downward from the atmosphere equal the infrared radiation emitted by the ground (Rg(t,0)(Wm-2)) plus the near-ground-surface conductive heat flux in the ground (G(t,0)(Wm-2)) plus the sensible heat flux to the atmosphere (H(t,0)(Wm-2)) plus the latent heat flux to the atmosphere (E(t,0) (Wm-2)).



Here, A is the surface albedo in the spectral range from visible to near infrared. If the surface temperature is Ts(t,0), Rg(t,0) is esT4s (t,0), where e is the emissivity of the ground, and s is the Stefan-Boltzmann constant, 5.67 x 10-8 Jm-2s-1deg-4.The phase difference between solar radiation and surface temperature is denoted by d. It is nearly 2 ~ 3 hours in summer. The conductive heat in the ground caused the delay. The pahse of conductive heat flux in the ground on the ground surface (z =0) is nearly the same as that of solar radiation. The phase difference d is also used for the conductive heat flux.

2.2 The balance of radiation at altitude z = 1.5m
Next, we considered the balance of radiation in an elementary slab of atmosphere of thickness dz at altitude z. The slab absorbs the incoming solar radiation (S(t,z) (Wm^-2)), the infrared radiation from the atmosphere directed downward (F¯(t,z)), the infrared radiation from the atmosphere directed upward (F­(t,z)), the infrared radiation emitted by the ground (R_g(t,z) (Wm^-2)), the solar radiation reflected by the ground (S(t,0) (Wm^-2)), the downward infrared radiation from the atmosphere reflected by the ground (F¯¯(t,0)) and the sensible heat flux from the ground to the atmosphere (H(t,z)(Wm^-2)). The slab emits infrared radiation downward (R_a¯ = K_inf rsT_a⁴ (t,z) 5/3 dz) and upward (R_a­).



Here r(Kgm^-3) is the density of absorber of the infrared radiation, k_vis and k_inf are the absorption coefficients for solar radiation and infrared radiation emitted by the ground surface or air, respectively. A mean thickness 5/3 dz is used for hemispheric radiation.