In the receiver's spotlight mode, the azimuth resolution
reaches 0.15 m.
Parameters Value Carrier frequency [f.sub.c] (GHz) 37.5 Bandwidth [B.sub.r] (MHz) 300 Height of platform H (m) 500 Velocity of platform v (m/s) 15 Pulse duration [T.sub.r] (us) 0.1 Pulse repeat frequency, PRF (Hz) 1000 Space distance of adjacent EPC d (m) 0.004 Number of transmitting antennas [N.sub.t] 10 Number of receiving antennas [N.sub.r] 11 Cross-track resolution (m) 4.5 Azimuth resolution
(m) 0.5 TABLE 2: Parameters of scatterers.
Parameter Description Value [f.sub.min] Minimum frequency 23.5 GHz [f.sub.max] Maximum frequency 24.5 GHz [PSI] Azimuth HPBW 33[degrees] [PHI] Elevation HPBW 17[degrees] [T.sub.P] Duration of chirp application-specific signal [DELTA][r.sub.ran] Range resolution 15.0 cm [DELTA][r.sub.azi] Azimuth resolution
1.3 cm (in SAR mode) [B.sub.acc] Bandwidth 50 Hz [s.sub.acc] Sensitivity 300 mV/g [N.sub.acc] Noise density 150 [micro]g/ [square root of Hz] [B.sub.gyr] Bandwidth 50 Hz [S.sub.gyr] Sensitivity 3.33 mV/[degrees]/s (4x amplified) [N.sub.gyr] Noise density 0.035[degrees]/s/ [square root of Hz] [DELTA] Bias drift within a 0.5[degrees]/s [[omega].sub.bias] temperature range of 10[degrees]C
In this paper, the azimuth resolution
degradation (defocusing) is analyzed since this effect is more important than the problem of the side lobes for the multi-look processing, especially for airborne SAR systems [5,6,21].
The swath of spaceborne SAR is restricted by azimuth resolution
, ambiguities of range and azimuth, signal-to-noise ratio, etc.
The measured azimuth resolution
after the improved MoCo is 1.1 m, better than the 1.2 m resolution after the sub-aperture approach.
In June 1951, Carl Wiley of Goodyear Aerospace Co, United States proposed the Doppler beam sharpening system which can be used to improve the azimuth resolution
of the radar.
Firstly, azimuth image merge is executed recursively to form a series of new subimages with improved azimuth resolution
2 times higher in azimuth direction each cycle during image merge process within the same range region; then new subimages of different range region are merged together through mosaic method to form the final image.
The sweeps integration increases the Signal-to-Noise Ratio (SNR), but it needs to be done carefully if the radar is not stationary and pointing in a fixed direction, because it can cause a defocusing of the radar picture (due to the reduction of the azimuth resolution
This allows for an improved azimuth resolution
with a very low pulse repetition frequency (PRF), thereby maintaining the swath width Another implementation of azimuth multichannel SAR that has been proposed is a constellation of formation-flying satellites .
A -3 dB beamwidth approximately equal to 22[degrees], as imposed by the constraint on the azimuth resolution
, is obtained in the copolar field.
Doppler beam sharpening (DBS) is an effective technique to improve the azimuth resolution
of airborne pulse Doppler radar in its air-to-ground mode.