The contradiction between azimuth resolution and swath is an important factor that restricts the performances for LEOSAR. Some advanced techniques are used in antenna to raise swath at present, and heightening SAR altitude is another approach to increase swath.
As described in Section 2.2, the Doppler bandwidth needed for MEOSAR can be less than LEOSAR for a given azimuth resolution.
Compared with LEOSAR, [R.sub.c] will be larger and [V.sub.s] smaller, so from Equation 7) we can see that the synthetic time for MEOSAR will be larger than LEOSAR for a given azimuth resolution.
For LEOSAR, synthetic time is usually less than one second, so ionospheric TEC can be considered as constant during the synthetic time and the effects induced by background ionosphere can be ignored.
For MEOSAR, both synthetic time and synthetic aperture increase a lot compared to LEOSAR, so the variance of TEC in the synthetic time cannot be neglected.
For LEOSAR, the cubic phase error is not generally considered, but the cubic phase error will increase a lot with the increase of synthetic time for MEOSAR.