Satellite Images vs Drone Photos

Recently, many case studies have been conducted on drone and map production with different techniques. One of these remarkable works was realized by GEOSCAN. The basis of the research is…
4 min read

Recently, many case studies have been conducted on drone and map production with different techniques. One of these remarkable works was realized by GEOSCAN. The basis of the research is to compare the satellite imagery to be used for mapping the white sea coast of Russia and the aerial photographs taken with the help of a drone. Now let’s take a look at this detailed study. High resolution optical systems are installed on low orbiting satellites. Currently, 14 satellites are available for commercial use. The feature of satellite imagery is that the resolution of the panchromatic (black-and-white image covering the blue, green, red and near-infrared part) is always higher than the resolution of the individual channels of the multispectral measurement. satellite data can analyze the condition of the coastline.
By processing a satellite image, it is possible to identify objects by varying the intensity of the representation of the different spectral channels or by creating different combinations of channels. In this study, Quadcopter Geoscan 401 is used for aerial photographs.
The Geoscan 401 also operates in the infrared range and is equipped with a Sony Cyber-shot DSC-RX1. It can take high quality aerial photos at 4 cm / pix high resolution.

Comparison of high resolution satellite images and UAV (unmanned aerial) air measurement data were performed on various criteria. Resolution The satellite panchromatic image used during the operation of the White Sea coastline has a spatial resolution of 46 × 46 cm.

The combination of channels in the multispectral range with the infrared channel makes it possible to identify various communities of vegetation. Geoscan 401 has a spatial resolution of 1 cm / Pix when the air scan is carried out at an altitude of 60 m. When a built-in geodetic receiver and ground control stations are used, it is possible to achieve an accuracy of up to 10 cm.

Alignment of a part of the 46 х 46 cm resolution panchromatic scan image (black and white image) of the WorldView-2 and the 1.0 х1.0 cm resolution image (color image) of the Geoscan 401 UAV.

Area Coverage
The area of ​​the satellite image frame is determined by the width of the research area. Disturbances and spatial resolution also depend on the angle of measurement. With the drone, the research area is determined by the type of drone, the resolution, the focal length and the distance from the starting area of ​​the research area. To avoid distortion, the images are captured with a large overlap. At a height of 60 m using a single battery for 60 minutes, the Geoscan 401 can take approximately 250 pictures during a single flight.
Most of the satellites designed for remote sensing are placed in orbit of the sun simultaneously. This means that images of the same zones will always be taken at the same time. With the use of drone, aerial photography can be done periodically at any time. The only requirement is that you have the necessary flight permits.
The acquisition time of the satellite images for any region is determined by the satellite’s flight time over the destination and the speed at which information is exchanged between service providers. The speed of the UAV air measurement is determined by the distance of the research area from the operator’s position and the proximity of the measurement area to access.
Weather Effects
The coincidence of high-quality satellite imagery in the clouds may have some undesirable consequences. However, it is possible to work with the drone in both open and cloudy weather.
Spectral Properties
The main measurement channels are common to all high-resolution satellites: there are 4 spectral channels, blue, green, red and near infrared, and a panchromatic channel. Aerial photographs obtained with the help of drones equipped with standard cameras are colored and visible spectrum. In addition, drones can be equipped with multispectral cameras, the quality of the images will be better than the satellite due to the higher resolution and lack of atmospheric distortions.
Shallow Water Depth Monitoring
In arctic seas, high resolution multispectral satellite imagery can detect large clusters of marine vegetation at depths of up to 1 meter. Unlike satellites, because the drone does not move away from the surface of the earth, atmospheric effects have no effect on image quality. Visibility under water is possible up to 7-10m. This allows the objects to be reliably distinguished at a depth of up to 5-6 m.

Some of the underwater objects clearly visible on the image of the Geoscan 401 UAV at a height of 50 m during low tide.

Track Changes
For tasks solved with the aid of high-resolution satellites, the interpretation of images with a resolution of 31 cm is sufficient. With the help of the drone, monitoring can be performed at a very detailed level. However, Drone’s range and flight time restricts the operation.
Spatial Data and Application in GIS
Multispectral satellite images are provided to the user as a set of files in GEOTIFF format. Each file contains a geographic reference image in one of the spectral channels. The images obtained from the aerial photographs taken with the use of the Geoscan 401 UAV are presented in RAW format files with geographic reference of the camera centers with 10 cm accuracy in WGS-84 coordinate system.
Software and Hardware
The most popular software packages for processing satellite imagery are currently ERDAS IMAGINE and ScanEx IMAGE. Due to the volume of the images, modern computers with large RAM and high processor speed are required to process satellite images. The Geoscan UAV can be installed both upright and obliquely with the included cameras. Processing of aerial photo data is performed in Agisoft Photoscan’s proprietary software and requires a high processor speed and a large amount of RAM because a large set of aerial photos is processed simultaneously.
While the integrated methods of the coastline of the seas with modern methods, both methods have positive aspects in their own way. However, we see that the use of drone stands out in many respects.

Click here to learn more about Geoscan 401 UAV.

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