Sensor

Optical vs SAR (synthetic aperture radar)

Optical sensors capture reflected sunlight. SAR sensors emit radar pulses and measure the echo — they see through clouds and at night.

Fig. 1 Optical sensors rely on reflected sunlight — they fail at night and beneath clouds. SAR (Synthetic Aperture Radar) is an active sensor: the satellite emits microwaves and measures the backscatter. Microwaves penetrate clouds, operate in darkness, and are sensitive to roughness and moisture rather than colour. SAR sees geometry; optical sees photons.

Optical sensors are cameras that record sunlight reflected off Earth's surface. They produce images that look like photographs. They cannot see through clouds and they do not work at night.

When SAR is the right answer

SAR sees through clouds and at night because it is radar, not a camera. The right answer when the AOI is persistently cloudy (tropical regions, monsoon seasons), when timing is critical and weather cannot be waited out (disaster response), or when you specifically need what SAR measures — surface deformation (InSAR), soil moisture, ship detection on open water, oil spill detection.

When SAR is the wrong answer

When you want something that looks like a photo. SAR imagery does not look like a photo — it is a speckled greyscale representation of surface roughness and dielectric properties, and interpreting it takes training. Geopera is currently optical-first.