Digital Rectification for Slar Imagery
1. Coordinate Equations of Radar Imagery
The coordinate equations of radar imagery for applying to digital processing is derived as Figure 2. Assume Ng is equal to Dg, it is called as the delay distance in which non-imagery is happened. The Y is for the scanning direction and the X is for the direction of flight of perpendicular to the Y through the point N. The point P, Pg and the arc (PPg) have the same range arc (PPg} have the same range (R) . If h is given, it is possible to work precisely out the ortho-position P of point P:
Fig. 2
x= X / Mx (1)
Y= [(Y2+h2-aHh)1/2 –Dg}/ My (2)
where Mx, My ------- scale denominator of the SLAR imagery It is easy to find both x and y or X and Y is independent each other in a side looking plane, and the imaging coordinates will be solved wit a DTM.
2. The Earth Curvature Influence
Because of the radar scanning of wide scope, it is neccessary to consider the earth curvature influence and correct it in each scanning line. The formulation as following:
dRe = [ ( H-h)2 + E2] 1/2 -R (3)
| E2 = r2 |
R2- (H-h)2
-------------------
(H+r) (r+h)
| (4) |
where
r----- the earth radius;
H----the antenna heigh;
h----elevation of groundpoint;
R----the range between the antenna and target.
3. Atmospheric Refraction Influence
The path of the microwave transmission is bent caused by atmospheric refraction, which is the same thing with the other electromagnetic waves. The path radius (r) is calculated following Lauyila’s formulations:
where R --- the earth radius, s—the range , A= a+b (H+h), a -3.7 X 10 and b= 1.4 X 10.
Here is only in consideration of the influvence for the different refractive indexes as following:
dRn = -sdn / r (6)
where dn----the difference between actual refractive indexes.
