Remote Sensing

Remote sensing is gathering information about a place without touching it. USGS defines it as "the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft)." NASA's Earthdata program says "Remote sensing is the acquiring of information from a distance," using instruments "on space-based platforms (e.g., satellites or spacecraft) and on aircraft that detect and record reflected or emitted energy."

Active and passive instruments

NASA divides sensors into two kinds:

• "Active instruments emit energy and collect data based on changes in the return signal." Synthetic aperture radar (SAR) is one; NASA says SAR "enables high resolution imagery to be created night or day, regardless of weather conditions."
• "Passive instruments detect energy emitted from the natural environment."

Resolution

NASA: "There are four types of resolution to consider for any dataset—radiometric, spatial, spectral, and temporal." Spatial resolution is "the smallest horizontal distance between successive elements of data in a dataset." Temporal resolution is "the time it takes for a space-based platform to complete an orbit and revisit the same observation area." NASA also notes that satellite data "require processing before the data are usable by most researchers and applied science users."

Mineral mapping

USGS uses imaging spectroscopy for critical minerals. "By measuring the absorption of light as a function of wavelength, spectrometers can identify minerals and chemical variations in minerals," and "Imaging spectrometers, commonly known as hyperspectral imagers, can map the distributions of minerals and variations in mineral chemistry at laboratory, field, and aircraft spatial scale." USGS's Earth Mapping Resources Initiative (Earth MRI) describes itself as "modernizing mapping of the Nation's surface and subsurface."

Change over time

USGS lists among uses "Tracking the growth of a city and changes in farmland or forests over several years or decades." Landsat imagery supports that kind of comparison; USGS refers to "working with Landsat data since it began in 1972."

Machine interpretation of imagery is covered under Computer Vision and Geospatial AI.

Why it matters for land and mining claim records

Imagery shows surface conditions on the date it was captured: roads, disturbance, structures, workings. It does not show ownership, mining claim status, or boundaries, which come from recorded documents and case files. Two properties of any image decide what it can support: its acquisition date and its spatial resolution. A feature smaller than the resolution will not appear, and a condition that began after the capture date is not there to see.