Earth observation satellites are spacecraft designed to measure conditions on Earth from orbit. They help scientists track forests, oceans, cities, ice sheets, storms, fires, and pollution over large areas. Because they repeat measurements over time, they reveal changes that are hard to see from the ground.
These satellites are essential tools for weather forecasting, disaster response, climate science, farming, and environmental protection.
Most Earth observation satellites operate in low Earth orbit, where they can view the planet in high detail while moving quickly around it. Their sensors detect reflected sunlight, emitted infrared radiation, radar echoes, or other signals from Earth’s surface and atmosphere. The data are converted into images or maps using calibration, geolocation, and computer processing.
Different wavelengths reveal different information, such as vegetation health, sea surface temperature, cloud structure, soil moisture, and surface elevation.
Key Facts
- Low Earth orbit is typically about 160 km to 2000 km above Earth’s surface.
- Orbital speed in circular orbit is v = sqrt(GM/r).
- Orbital period is T = 2πsqrt(r^3/GM).
- Spatial resolution is the smallest ground feature a sensor can distinguish, such as 10 m per pixel.
- Electromagnetic wave relation: c = λf, where c is wave speed, λ is wavelength, and f is frequency.
- Sun-synchronous satellites pass over the same location at nearly the same local solar time, improving comparisons over days, months, and years.
Vocabulary
- Remote sensing
- Remote sensing is the measurement of objects or environments from a distance using reflected or emitted energy.
- Low Earth orbit
- Low Earth orbit is a region close to Earth where satellites move rapidly and can collect high-resolution observations.
- Spatial resolution
- Spatial resolution is the ground size represented by one image pixel or the smallest detail a sensor can separate.
- Spectral band
- A spectral band is a selected range of wavelengths measured by a satellite sensor.
- Swath width
- Swath width is the width of Earth’s surface observed by a satellite during one pass.
Common Mistakes to Avoid
- Confusing spatial resolution with image size is wrong because a larger image can still have poor detail if each pixel covers a large ground area.
- Assuming satellites can always see through clouds is wrong because visible and infrared sensors are blocked or distorted by clouds, while radar is often needed for all-weather imaging.
- Treating every satellite image as a natural-color photograph is wrong because many Earth observation images use infrared, microwave, or false-color bands to show information invisible to human eyes.
- Ignoring orbit type is wrong because altitude, inclination, and repeat cycle strongly affect resolution, coverage, and how often a location can be observed.
Practice Questions
- 1 A satellite orbits at an altitude of 700 km. Using Earth’s radius as 6370 km, find the orbital radius measured from Earth’s center in kilometers.
- 2 A sensor image has pixels that each represent 30 m by 30 m on the ground. What ground area, in square meters, is covered by one pixel? How many square meters are covered by 1000 pixels?
- 3 Explain why a climate-monitoring satellite might use multiple spectral bands instead of only taking visible-light images.