Passive remote sensors measure ambient energy (typically generated by the sun) that is reflected off a surface. These sensors measure the whole breadth of the electromagnetic spectrum, with most sensors measuring visual (red, green, blue), near-infrared, and infrared (thermal) energy.
Passive remote sensors are typically selected because of their positive characteristics when compared to active remote sensors including their:
- Low cost
- Low weight
- Minimal power consumption
The primary hindrance to passive remote sensors is their reliance on ambient energy conditions. Factors such as cloud-cover can severely limit or ruin a data set.