Types of Satellites
There are several different types of satellites that are used for a variety of purposes. Some common types of satellites include:
- Communication satellites: These satellites are used to transmit and receive signals for telecommunications, such as phone calls, internet data, and television broadcasts.
- Navigation satellites: These satellites are used for positioning, navigation, and timing (PNT) purposes, such as the Global Positioning System (GPS).
- Earth observation satellites: These satellites are used to collect data about the Earth’s surface and atmosphere, including images and other types of data, for a variety of applications, such as mapping, environmental monitoring, and weather forecasting.
- Weather satellites: These satellites are specifically designed to collect data about the Earth’s weather and climate, including temperature, humidity, and atmospheric conditions.
- Military satellites: These satellites are used by military forces for a variety of purposes, including communication, navigation, intelligence gathering, and surveillance.
- Scientific research satellites: These satellites are used to conduct scientific research and experiments, such as studying the Earth’s atmosphere or the effects of space on human health.
Overall, there are many different types of satellites that serve a wide range of purposes, from practical applications like telecommunications and navigation to scientific research and military operations.
There are several types of platforms that can be used to carry remote sensing sensors on satellites:
- Low Earth orbit (LEO) platforms: These satellites orbit the Earth at an altitude of a few hundred kilometers, and are typically used for applications that require high spatial resolution (e.g. less than 1 meter). The relatively low altitude of these satellites means that they can capture detailed images of the Earth’s surface, but they only cover a small area with each pass and therefore need to be frequently revisited to cover larger areas. Examples of LEO platforms include the Landsat and Sentinel series of satellites.
- Medium Earth orbit (MEO) platforms: These satellites orbit the Earth at an altitude of several thousand kilometers, and are typically used for applications that require moderate spatial resolution (e.g. 10-30 meters). MEO satellites provide a larger coverage area than LEO satellites, but with lower spatial resolution.
- Geostationary orbit (GEO) platforms: These satellites orbit the Earth at an altitude of about 36,000 kilometers, and remain stationary relative to a specific point on the Earth’s surface. GEO satellites are typically used for applications that require continuous monitoring of a specific region, such as weather forecasting or communication.
- Polar orbit platforms: These satellites orbit the Earth in a north-south direction, crossing the poles with each pass. Polar orbit satellites are typically used for applications that require global coverage, such as the monitoring of the Earth’s atmosphere and oceans.
Overall, the choice of platform for a satellite remote sensing mission depends on the specific requirements of the application, including the spatial resolution and coverage area needed and the type of data being collected.
Satellite Characteristics: Orbit and Swaths
The orbit of a satellite refers to the path that it follows around the Earth or other celestial body. Satellites can be in various types of orbits including low Earth orbit (LEO), medium Earth orbit (MEO), geostationary orbit (GEO), and highly elliptical orbit (HEO).
Low Earth Orbit (LEO): LEO is an orbit at an altitude of around 100 to 2000 kilometers above the Earth’s surface. Satellites in LEO are closer to the Earth and therefore have a shorter distance to travel for communication. However, they also experience more atmospheric drag and need to be replaced more frequently. Examples of LEO satellites include the International Space Station and weather satellites.
Medium Earth Orbit (MEO): MEO is an orbit at an altitude of around 8,000 to 12,000 kilometers above the Earth’s surface. Satellites in MEO have a longer distance to travel for communication compared to LEO satellites, but they also experience less atmospheric drag and have a longer lifespan. Examples of MEO satellites include navigation satellites such as GPS.
Geostationary Orbit (GEO): GEO is an orbit at an altitude of around 35,000 kilometers above the Earth’s surface. Satellites in GEO orbit at the same speed as the Earth’s rotation, so they appear to be stationary in the sky. These satellites are often used for communication and television broadcasting.
Highly Elliptical Orbit (HEO): HEO is an orbit that has a high degree of ellipticity, meaning it has a large difference between its closest and farthest points from the Earth. Satellites in HEO have a long period of time at a high altitude and a short period of time at a low altitude. They are often used for communication with polar regions or for military surveillance.
The swath of a satellite refers to the area on the Earth’s surface that it can cover in a single pass. Swath width is determined by the satellite’s resolution and its altitude. Satellites with higher resolution and lower altitudes will have a smaller swath width, while satellites with lower resolution and higher altitudes will have a wider swath width. Satellites with wide swath widths are useful for covering large areas quickly, while satellites with narrow swath widths are useful for detailed analysis of specific areas.
Scanning Method: Image & Video
The process of using satellite and sensors to scan images and video involves several steps:
- First, a satellite or sensor is launched into orbit around the Earth. These devices are equipped with specialized cameras and other sensors that are capable of capturing images and video from high above the Earth’s surface.
- The satellite or sensor then begins to collect data on the area that it is tasked with scanning. This could be a specific region, such as a city or a natural disaster zone, or it could be a wider area, such as a continent or even the entire planet.
- The collected data is transmitted back to a ground station where it is received and processed. This typically involves converting the data into a usable format, such as a series of still images or a video.
- The processed data is then analyzed by scientists and researchers to gain insights into the area being studied. This could include things like mapping out land features, monitoring changes in vegetation, or tracking weather patterns.
- The results of the analysis are then used for a variety of purposes, such as disaster response, environmental monitoring, or military intelligence.
Overall, the use of satellite and sensor technology is an important tool for understanding and studying the Earth and its many complex systems. It provides a unique perspective that allows researchers to see and understand things that would be difficult or impossible to study from the ground.
FOV & IFOV
FOV (Field of View) refers to the angular range of an imaging sensor or camera that can be captured in a single image. It is typically measured in degrees and can vary depending on the size and type of the sensor or camera. For example, a wide-angle lens may have a FOV of 100 degrees, while a telephoto lens may have a FOV of 30 degrees.
IFOV (Instantaneous Field of View) refers to the angular field of view of a single pixel within an imaging sensor or camera. It is typically much smaller than the overall FOV of the sensor or camera, as it is based on the size of the individual pixels rather than the overall size of the sensor or camera. For example, an imaging sensor with a FOV of 100 degrees may have an IFOV of 0.001 degrees for each pixel.
In satellite imaging, the FOV of the sensor or camera is important because it determines the area that can be captured in a single image. A wider FOV allows for a larger area to be captured, while a narrower FOV allows for higher resolution images of a smaller area. The IFOV is also important because it determines the spatial resolution of the image, with smaller IFOV values resulting in higher resolution images.
Spatial, Spectral, Radiometric and Temporal – Spatial resolution refers to the ability of a satellite or sensor to distinguish objects or features on the ground. It is typically measured in meters or pixels and determines the level of detail that can be captured in an image.
Spectral resolution refers to the ability of a satellite or sensor to distinguish different wavelengths of light, such as different colors in the visible spectrum or different bands in the electromagnetic spectrum. This is important for identifying specific materials or features on the ground.
Radiometric resolution refers to the ability of a satellite or sensor to accurately measure the intensity of light being reflected or emitted from the ground. This is important for accurately interpreting the data collected by the satellite or sensor.
Temporal resolution refers to the frequency at which a satellite or sensor captures images or data. A satellite or sensor with high temporal resolution will be able to capture images or data more frequently, allowing for more up-to-date information to be gathered.
Hyper Spectral Sensors and Imaging
Hyper spectral sensors and imaging are advanced technologies used in satellite and sensors to gather detailed information about the composition and characteristics of the Earth’s surface. These technologies use a range of wavelengths in the electromagnetic spectrum to capture images of the surface, providing information about the different materials and substances present.
Hyper spectral sensors use a series of narrowband filters to capture images at specific wavelengths, allowing for the identification and classification of different materials based on their unique spectral signatures. This information can be used for a variety of applications, including environmental monitoring, resource management, and military surveillance.
Imaging systems, on the other hand, use a combination of visible and infrared wavelengths to create detailed images of the surface. These images can be used to detect changes in land cover, identify features such as vegetation, water bodies, and buildings, and monitor the health of crops and forests.
Hyper spectral sensors and imaging are key components of satellite and sensor systems, providing valuable data for a wide range of applications. These technologies are helping to improve our understanding of the Earth’s surface and the processes that shape it, and are playing an increasingly important role in decision making and resource management.
Pixel Size and Scale
Pixel size refers to the physical size of each pixel (or picture element) on a satellite sensor. This size can vary depending on the specific sensor and satellite being used. Scale refers to the size of an object or feature on the ground as it appears on a satellite image. For example, a small-scale image may show a large area but with less detail, while a large-scale image may show a smaller area but with more detail.
Both pixel size and scale are important factors to consider when analyzing satellite imagery, as they can affect the resolution and accuracy of the data. For example, a sensor with a smaller pixel size may be able to capture more detailed images, but may also be more expensive to operate. Similarly, a large-scale image may provide more detailed information about a specific area, but may not cover as wide of an area as a small-scale image.