Final answer:
The three methods used in passive remote sensing are visible-light detectors, infrared detectors, and microwave detectors.
Step-by-step explanation:
The three methods used in passive remote sensing are:
- Visible-light detectors: These include the human eye, photographic film, and charge-coupled devices (CCDs).
- Infrared detectors: These detectors are sensitive to infrared radiation and must be cooled to very low temperatures.
- Microwave detectors: Most satellite-transmitted information is carried on microwaves, and radar is a common application of microwaves.