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1. Independence of solar illumination

Independence of solar illumination SAR is an active system.

It illuminates the Earth surface and measures the reflected signal. Therefore, images can be acquired day and night, completely independent of solar illumination, which is particularly important in high latitudes (polar night).
The Netherlands This SAR image was acquired by ERS-1 on 2 August 1991 over the Netherlands, local time 23:40.

2. Independence of cloud coverage

Independence of cloud coverage The microwaves emitted and received by ERS SAR are at much longer wavelengths (5.6 cm) than optical or infrared waves. Therefore, microwaves easily penetrate clouds, and images can be acquired independently of the current weather conditions.
Udine These images were acquired over the city of Udine (I), by ERS-1 on 4 July 1993 at 9.59 a.m. (GMT) and Landsat-5 on the same date at 9.14 a.m. (GMT) respectively. The clouds that are clearly visible in the optical image, do not appear in the SAR image.