What is a satellite?
A satellite is a man-made object that is sent into orbit around the Earth, or around another planet or celestial body. The purpose of a satellite can vary depending on its design and mission, but generally, they are used for a variety of tasks such as:
- Communication: Satellites are used to transmit and receive signals for various forms of communication, such as television, radio, telephone, and the internet.
- Observation: Satellites can be equipped with cameras and other sensors that are used to observe and collect data about the Earth’s surface.
- Navigation: Satellites are used to determine the precise location of objects on the Earth’s surface through a system called Global Positioning System (GPS)
- Other applications: such as scientific research, military operations, reconnaissance and many other tasks require the ability to see or communicate with the Earth from space.
When people talk about Multispectral and Hyperspectral Satellites they are talking about earth observation satellites
What is the difference between Multispectral and Hyperspectral Satellites
The main difference between the two is in the number of wavelength bands that they measure.
What is a wavelength band?
In remote sensing, the electromagnetic spectrum is usually divided into different regions, or bands, each corresponding to a specific range of wavelengths. These regions are called “wavelength bands” or “spectral bands” and they allow the collection of data in specific ranges of the electromagnetic spectrum.
These bands are chosen because they have a specific interaction with the materials and surfaces on Earth, and can provide information about the composition and characteristics of the objects on the ground.
Multispectral satellites typically have a smaller number of wavelength bands, usually less than 20, and are often used for applications such as crop mapping, land cover classification, and mineral identification.
Hyperspectral satellites, on the other hand, have a much larger number of wavelength bands, often more than 100, and are used for more specialized applications such as the identification of specific minerals or chemicals in the environment, oil and gas exploration, and military surveillance.
Because hyperspectral satellites have a finer spectral resolution, they can detect very subtle variations in the reflected or emitted radiation and can identify individual chemicals or minerals with high accuracy. Multispectral satellites, however, are less expensive to build and operate and provide less detailed data.
When a satellite or other instrument is said to have a “fine” or “high” spectral resolution, it means that it can detect small differences in the wavelength of the electromagnetic radiation it is measuring.
Hyperspectral satellites are equipped with a large number of detectors, each of which is sensitive to a very narrow range of wavelengths. These detectors work together to collect data across a wide range of the electromagnetic spectrum. The resulting data provides information about the composition and characteristics of the objects or materials on the ground in much greater detail than multispectral satellites.
In other words, a high spectral resolution allows a hyperspectral satellite to capture more detailed information about the reflected or emitted radiation.
It is worth mentioning that spectral resolution is one aspect of a hyperspectral instrument. Spatial resolution, signal-to-noise ratio, radiometric resolution, and other parameters play important roles as well depending on the observation goal and application.
In general, the spatial resolution of multispectral satellites is coarser than that of hyperspectral satellites. This is because multispectral sensors typically use a single detector to collect data for multiple wavelength bands at once, this implies a lower number of detectors and thus a wider field of view which in turn results in a bigger pixel size. The resulting image will have a lower spatial resolution compared to a hyperspectral sensor.
|Multispectral satellites||Hyperspectral satellites|
|Number of wavelength bands||Less than 20||More than 100|
|Cost to build and operate||Moderate||High|
|Applications||Wide range, ex. crop mapping, land cover classification, mineral identification||Specialized, ex. identification of specific minerals or chemicals, military surveillance|
It’s worth noting that this table is only an example and that the values of each category can vary depending on the specific instrument and mission.