Remote sensing methods are methods of studying the Earth and other space bodies from air or spacecraft with the help of aerial photography and satellite imagery. Satellite and aerial imagery help explore landscapes, analyze the scale of human impact on the environment, and find inspiration in the mesmerizing textures, shapes, and patterns on the planet’s surface: natural or human-made.
The similarity between aerial photography and space imagery is that both are carried out from an aircraft, from a height. The principle of operation of the sensors used also turns out to be similar. Later, these images are collected and analyzed by different experts to pull out the necessary data. Besides, other online tools like LandViewer help search and download such imagery already analyzed for various purposes.
Of course, there are differences between satellite and aerial photography. Space imagery is carried out from an altitude much higher than aerial photography. In terms of the quality of frames, space imagery may be even of a higher resolution because it uses entirely digital equipment. But aerial photography is less dependent on cloud cover since it can be carried out from a lower height. Besides, satellite imagery covers a larger area and takes less time to create a complete map than aerial imagery. However, aerial photography can be more accurate than satellite pictures because it creates the map closer to the real scale, making it more recognizable than a satellite image.
So how do you choose which type of imagery is more fit to your needs? Do you need high-resolution images or a lower resolution will be enough? That depends on the different factors that we are going to cover in this piece. But first, let’s define satellite and aerial photography.
What is Satellite Imagery?
Satellite imagery is pictures of our planet taken by satellites located outside the Earth’s atmosphere. Satellites use specific sensors to detect electromagnetic radiation reflected from the Earth. There are two types of sensors mounted on the satellite for this purpose. Passive sensors register radiation emitted by the Sun and reflected from the Earth’s surface. Active sensors, on the contrary, emit electromagnetic radiation themselves and are irreplaceable in many cases since they can be used at any time of year and day, contrary to passive sensors that can be used only at day-time when the sunlight is present.
One of the main characteristics of a satellite image is its spatial resolution. It is expressed in the size of the most miniature objects visible on the image. The image consists of individual colored dots – pixels. The fewer meters on the ground fit into one pixel, the higher the resolution and the more detailed the obtained picture.
Depending on the resolution, there are three types of satellites:
- High-resolution satellites. They are used for detailed land study, ships detection, construction planning, natural and human-made disasters forecasting, etc. In forestry, such images enable the detection of individual trees and even identification of their species. This can be useful when tracking illegal logging in cases where only several valuable trees are cut down.
- Medium-resolution satellites. Used for updating topographic maps, forest management, natural phenomena forecasting (floods, forest fires, oil spills), solving many agricultural problems (tracking crop health, forecasting yields).
- Low-resolution satellites (several kilometers per pixel). Such images are used to study the atmosphere and cloud layer, a compilation of meteorological maps, determination of the temperature of the surface of the land and ocean for tracking ice cover and forest fires.
While humans can only see a small portion of the electromagnetic spectrum (visible light), satellite sensors also use other types of electromagnetic radiation, such as infrared light, ultraviolet radiation, radio waves, and even microwaves. Rocks, soil, water, vegetation reflect and absorb electromagnetic waves in different ways. This allows for receiving satellite imagery suitable for analysis by players of various industries.
What is Aerial Photography?
Aerial photography involves photographing an area from a height of hundreds of meters to tens of kilometers using an aerial camera mounted on an aircraft (airplane, helicopter, airship, drone).
Earlier, aerial photography required flying a real plane or helicopter, which implied receiving flight permits, paying for expensive fuel and work of pilots, and much more. Now, equipment for aerial photography can be brought in the trunk of any car. Modern drones are used in different spheres of human lives, finding applications in various industries, including agriculture, forestry, and much more.
Choosing Between Aerial and Satellite Imagery
Ultimately, aerial photography and satellite imagery offer a view of the ground and its features and objects from above. Both find use in different spheres that require geospatial data. Aerial photography is more suitable across commercial applications, while satellite imagery is more convenient for large-scale scientific applications.
Each possesses unique characteristics and advantages. So, how do you choose between them? There are some key parameters to consider before opting for satellite or aerial imagery:
- Resolution. The highest commercially available resolution for satellite imagery is 30 cm, while the aerial imagery resolution can go up to 2.5 cm depending on the application.
- Data type. Most aerial cameras provide a fourth near-infra-red band of imagery and standard RGB bands. At the same time, modern satellites possess additional optical bands designed for specific applications, such as vegetation analysis.
- Weather. Contrary to satellite imagery, aerial photography guarantees cloud-free data delivery and allows for planning data collection according to the local weather conditions.
- Location accuracy. The typical accuracy of aerial imagery is 1/5,000th and 1/8,000th of the height from which they were taken, while high-resolution satellites offer location accuracy of approximately 10m.
- Cost. Satellite imagery acquisition costs are usually lower than aerial imagery costs since they do not require buying the equipment and spending money to get to the destination that requires monitoring. The prices of satellite images vary depending on the satellite data provider or the app you are using for this data acquisition and analysis.
All in all, to choose between aerial or satellite imagery, it’s necessary to understand the purpose of their use, the data that needs to be retrieved, the location, the depth of future analysis of the image, and the cost the user is willing to pay.