743 
Table 2. ATLAS database layout 
Station ID 
FileName 
Obs_Date 
Obs_Time 
Sol_Zen 
Sol_Azm 
View_Ang 
View_Azm 
TB3 
A102304 
17-SEP-92 
10:23:04 
23.045 
108.765 
-15.00 
108.77 
TB3 
A102313 
17-SEP-92 
10:23:13 
22.955 
108.804 
-30.00 
108.77 
TB3 
Al02320 
17-SEP-92 
10:23:21 
22.734 
108.921 
-45.00 
108.77 
TB3 
A102332 
17-SEP-92 
10:23:32 
22.605 
109.002 
-60.00 
108.77 
FOV 
Hemisphere_ID 
Data_Type 
Data_Units 
Obs_Mode 
Descriptor 
1 deg 
GROUND 
Reflectance 
% 
6 
Tiger Bush Soil SPP 
1 deg 
GROUND 
Reflectance 
% 
6 
Tiger Bush Soil SPP 
1 deg 
GROUND 
Reflectance 
% 
6 
Tiger Bush Soil SPP 
1 deg 
GROUND 
Reflectance 
% 
6 
Tiger Bush Soil SPP 
Chi Data 
Ch2 Data 
Ch3_Data 
Ch251_Data 
Ch252_Data 
Rev_Date 
5.42 
6.75 
6.92 
5.62 
4.70 
17-FEB-93 
3.57 
6.45 
6.40 
// 
5.34 
3.20 
17-FEB-93 
5.78 
7.34 
7.56 
5.76 
4.71 
17-FEB-93 
5.44 
7.28 
7.40 
5.44 
4.55 
17-FEB-93 
Table 3. ATLAS Observation Modes 
Obs_Mode 
Description 
0 
Undefined 
1 
Solar disk 
2 
Solar almucantar 
3 
Vertical profile 
4 
All sky scan 
5 
Nadir 
6 
Solar Principal Plane 
7 
Set azimuth plane 
8 
Full BRDF 
2.5 Calibration 
2.5.1 In-Field Calibration. During field deployment periodic inter-calibration of the heads was made by using a 
Spectralon calibration panel and taking measurements with both 1* and 15’ FOVs for comparison with the 
global irradiance collected simultaneously with the cosine corrected head. Spectral calibration was also checked 
on a regular basis by using a Didymium filter held in front of each of the heads which imparts a set of absorption 
features of known wavelengths onto the recorded spectrum. 
2.5.2 Laboratory Calibration. Laboratory calibration was carried out following the IOP at the Equipment Pool 
for Held Spectroscopy (EPFS) at the University of Southampton using an integrating sphere of known output for 
the 1' and 15’ FOV heads and a calibrated spectral lamp for the cosine head. Calibration measurements were 
carried out at all the integration times used during the field experiment to assess linearity of the instrument 
electronics. The calibration values of the integrating sphere and lamp have subsequently been verified and traced 
to a national standard held by the National Physics Laboratory (NPL) and calibration of the 7,500 spectra is now 
proceeding. 
3. PRELIMINARY RESULTS AND MODELLING 
3.1 Atmospheric Optical Parameters 
3*1.1 Optical Depth. As stated above, the lack of direct beam solar irradiance has severely hindered the 
validation of a number of algorithms being developed to retrieve atmospheric optical depths and thence derive a 
number of aerosol optical parameters required as input to radiative transfer models and for correction of the