A study of calibration technique for side looking Airborne Radar
Experiment
As has been obtained above
s° is proportional p
r/p
t0. Further more is no need for separate measurement of transmitter power and receiver characteristics, and it needs only the direct measurement of it's value when a sample of the transmitted signal is used to calibrate the receiver. As far as the SLAR is concerned, it is very easy to realize. The experimental block diagram and data is shown in Fig. 1
Where
| Working wavelength |
l = 3.2cm |
| Antenna type |
Slot array antenna with pattern of CSC2j |
| peak power |
Ptc>50KW |
| Pulse width |
t = mS |
| Pulse repeating frequency |
Fr = 1Kc |
| Receiver characteristics |
FI = 60MC, GIF>80db. Nf<9db |
| Photographical instrument |
Device changed electricity into light width
optical optical fiber revcording tube |
| Flying altitude |
H = 3000m |
A directional coupler C
t is set between transmitter and antenna feline and another C
r between antenna and receiver feed line. And an attenuator between the C
t and C
r is a known attenuator of L
c, so that a sample of transmitter signal may be feed through the receiver. Assuming that the value of the transmitter power at the directional coupler C
t is P
t and received power at the another C
r is P
r. As long as the transmission line loses L
t and L
r and the antenna gains remain constant, the calibration using the sample of the transmitted signals gives a complete relative calibration of the SLAR system.
The value for calibration signal P'
rc at the output of the receiver direction coupler is given by
P'rc = P'to/LcCtCr
The out put power for the calibration signal with receiver gain si given by
Poc = grPrc
The output indication for the received signal is given by
Per = grP'r
With systemization above expression it is obtained by
Por / Poc = P'r / P'rc = ( P'r / Prc )LcCtCr
Since
Pto =P'to/Lt
Pr = Pr Lr
When this is substituted in above expression, the scattering cross section becomes
s° = [(4p)3R4 / G20l2Aop] . [LrLt / LcCtCr] . [(Por/Poc)
Thus under the trigger pulse from synchronizator with a definitive width, the cycial radio frequency power illuminates the area passing through the directional coupler C
t, and antenna
Duplexer Tr/ATR. When the antenna duplexer TR/ATR is open to receiving channel, the samples from transmitter signal feed into receiver and there si change from electricity into light by photographical instrument and is sensed automatically on film. After the pulse, antenna duplexer is automatically opened from transmission channel and is insulated to receiving channel. Simultaneously with this, the value of transmission sample is equivalently opened to receiving channel as well.
Thus, as long as return power form calibration target going to the receiver and change electricity into light pass through photographical instrument and is sensed on film as well as. Finally, one can obtain proportional value of two output indication by micro densityer or density cut instrument.
Evidently, the
s° of any calibration target is obtained by following expression for the SLAR imaging swath width, and the aim of quantitiative remote sensing technique can be obtained.
s° = [(4p)3R4/G2ol2Awp] . [LtLr/LcCtCr] . (Porp/Poc]
When R
n is easily counted by geometry relationship as shown in Fig 2
Where
Rn = [H2+(ro+rdn)2]½
Where
| H |
Altitude of the SLAR platform |
| r0 |
The width of blind area of the SLAR |
| rdn |
Distance between the boundary of the SLAR blind area
and calibration target to be detected. |
References
- Meng Kan, Microwave Remote Sensing, Inter Chinese Institute of Technology Publishing House, 1982.
- Fawwas T. Ulaby, Richard K. Moore, Adrian K. Fung, Microwave Remote Sensing : Active and Passive, Vol.2, Addison-Welsley Publishing Company in USA 1982
- Robert G. Reeves, Manual of Remote Sensing American Society of Photogrammetry, Volume 3m, 1975.
- H.D. Brunfeldt, F.T Ulbay, Performance Analysis of the Microwave Remote Sensing Active Spectrometer systems : Calibration, precision and accuracy" Remote Sensing Lab, University of Kasas, 1979.
