S 
acebourne/ ground 
ing spectral indices 
>rrain surfaces. 
jectral bands in the 
>1d instrument. 
n the radiometric 
T-p). 
corrections and for 
rmalized difference 
en in Table 3. 
  
te any two bands in 
400 nm to 1800 nm. 
ands as follows 
Band width 
40 
155 
g outputs go to data 
allel. 
ftware is designed to 
on and temperature 
| indices viz. Ratio 
transferred from Data 
npatible machine. 
adiance 
-Sr-) 
ted with software) 
  
IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India,2002 
  
  
9.1 Optical head +18 Voltsat5 mA 
92 Display unit/ 
Data Logger: +9 V, 20 mA 
10. Size: 100 mm * 100 mm * 180 
11. Weight (kg): 3:5 
12. Environmental conditions: 
12.1 Operating 
temperature (°C): Oto 50 
122 Storage 
temperature (°C): Oto 70 
12.3 Humidity RH (%): 30 to 90 at 40 °C 
  
  
  
Table 3. Specifications of Ratio Radiometer 
5. DESCRIPTION 
Functional block diagram of the ratio radiometer is shown in 
Figure 1. The instrument is a combination two modules for two 
individual spectral bands. Both the modules are mounted in a 
common frame structure. The instrument and modules are easy 
for mechanical fabrication. Each module has the components: a 
mechanical field-of-view (FOV) assembly, interference filter, 
and detector and associated processing electronics. Each field- 
of-view assembly essentially consists of a set of apertures that 
forms the desired field of view of 15 degree. The overall 
dimensions of the field-of-view assemblies are kept optimal to 
raiViisible channel 
  
  
  
  
  
  
| I -eardndrared channel 
  
  
absorb all the scattered radiations within the field of view and 
absorb unwanted radiation outside the field of view. 
Interference filters have been incorporated to select any desired 
spectral bands. Silicon and germanium photodiodes have been 
incorporated to detect the input optical power in two bands. The 
spectral response for silicon detector is from 350 nm to 1100 
nm while for germanium detector is from 800 nm to 1800 nm. 
The detectors have been shielded properly to avoid any 
background radiations by mounting them inside the cavities. 
Detectors, field-of-view assemblies, and interference filters are 
optically aligned. Both the modules are FOV registered, so that 
they look the same target areas at a distance of one meter. The 
analog signals produced by the detectors are processed with the 
processing electronics. The analogue outputs from these two 
bands go to a standard data logger where data is stored along 
with house keeping information. The data logger is auto 
ranging that covers four decades of voltage range from 10 mv 
to 10 v with the resolution of 14 bits. It has linearity of + 
0.05%, accuracy of + 0.03%, and temperature coefficient of + 
0.01% of reading per degree centigrade. The data logger also 
stores the date and time stamps along with every logged data. 
The data and house keeping information stores in a sequential 
manner. The data stored in data logger would be transferred to 
PC with RS 232 interface and processed subsequently with 
specially designed software. Execution of software program 
generates an output file containing corrected outputs with 
respect to offsets and temperatures, and spectral indexes: ratio 
index and normalized difference index and other house keeping 
/ field information. 
Electronic 
Mm Processing PCB 
Detector | 
  
  
  
Fig 1. Functional block diagram of Ratio Radiometer 
  
6. RADIOMETRIC CALIBRATION 
The instrument was calibrated in a radiometric quantity of 
spectral radiance with a standard source. The calibration 
standard is "OL Series - Integrating Sphere Calibration 
Standard”, S/N 95201250. Optronic Laboratories, Inc. USA 
(Optronic Laboratories, Inc., 1996). The standard source has 
been supplied along with the calibration certificate (Optronic 
  
Laboratories, Inc., 1996). The standard is traceable to National 
Institute of Standards and Technology (NIST), USA. The 
standard consists of a 150 watt quartz tungsten halogen lamp 
driven by a constant current power supply and an integrating 
sphere to get Lambertian output spectral radiance. The source 
has capability to produce continuous radiant flux in the 
wavelength range, from 350 to 2500 nm. The aperture setting of 
the standard produces an output in 6 decades of dynamic range.