Remote sensing means measuring the Earth's surface from a distance: from a satellite, an aircraft or a drone. For forest and carbon projects it is the main way to see a whole site at once and on a regular schedule.
What a satellite sees
A satellite records light reflected from the surface in several spectral bands. The human eye sees only visible light, while remote sensing instruments also work in the near, mid and thermal infrared. Healthy vegetation strongly reflects near-infrared light and absorbs red light, so the ratio between bands tells you its condition.
The NDVI index
The best-known indicator is NDVI, the Normalized Difference Vegetation Index. It is calculated as (NIR − Red) / (NIR + Red), where NIR is the near-infrared band and Red is the red band. Values close to 1 mean dense, healthy vegetation, values near 0 mean bare soil, and negative values mean water.
Resolution and revisit
Spatial resolution is how many metres of ground fit into one pixel. At 10 m/pixel you see fields and forest stands; at 1 m/pixel you see individual crowns. The revisit cycle is how often a satellite images the same site: the shorter it is, the sooner a fire, logging or dying plantings show up.
How remote sensing helps measure carbon
By linking spectral indicators to ground measurements, models estimate biomass and carbon stock for every plot. Repeat imaging shows the change in stock, that is, how much carbon was absorbed over a period. This is exactly the data MRV needs — the monitoring, reporting and verification of carbon credits.
Drones complement satellites where you need tree-level detail: canopy layer density, micro-relief and the condition of young plantings.