Aerospace optical remote sensing technology: Earth's all-around "selfie tool"

The application of aerospace optical remote sensing technology is indispensable in the process of satellite image acquisition. Optical remote sensing satellites can be described as "selfie cameras" specially designed for Earth, and as optical remote sensing satellite images enter civilian and commercial systems, Earth's "selfies" will play an even greater role in many fields.

Space optical remote sensing technology: detecting the ground or celestial bodies from high altitudes.

Space optical remote sensing technology generally refers to the technology of detecting ground targets from an altitude of more than 100 kilometers or above, or detecting celestial bodies from high altitudes, in order to obtain relevant information.

Using artificial satellites, space stations, or space shuttles as space carriers, and optical remote sensing equipment such as space cameras, scanners, or imaging spectrometers that use visible light (or) ultraviolet and infrared radiation as payloads, aerospace optical remote sensing uses optical systems to collect radiation reflected from and emitted into space by ground objects. This radiation is then converted into electrical signals by photodetectors, and further processed through storage and data analysis to obtain spatial, temporal, and spectral information about ground objects, providing users with information for analysis, monitoring, and identification.

Principles of Aerospace Optical Remote Sensing Technology

After the Earth's surface is irradiated by sunlight, the reflected light carrying the surface image information passes through the atmosphere and enters the optical remote sensor. On the image plane of the optical system, an image of the target scene is formed and received by the receiver. After further processing, an image product can be obtained.

In the ultraviolet, visible, and infrared remote sensing bands, optical remote sensing technology can generate common optical images such as panchromatic images, visible light images, and multispectral/hyperspectral data. Visible light and panchromatic images, with their high spatial resolution, provide clear spatial texture information for observed targets. Multispectral/hyperspectral data has the advantage of combining spectral images, revealing the essential characteristics of ground features. Different types of ground features exhibit different spectral curves due to differences in their electromagnetic wave reception and radiation characteristics. Optical remote sensing image classification is based on the spectral characteristics of pixels, falling under the category of pixel-level classification.

Main instruments for aerospace optical remote sensing technology

Based on the type of image information, the optical instruments used in aerospace optics are divided into two categories: one is used to obtain black and white images of ground targets, called panchromatic cameras or full-spectrum cameras, which mainly provide the spatial characteristics of the targets; the other is used to obtain images at multiple different spectral bands, called hyperspectral/multispectral imaging or imaging spectral cameras.

• Panchromatic imaging camera

A panchromatic camera is a telescope that can collect information about ground points in the visible light band. After being converged by the telescope, a panchromatic image of the target is formed on the focal plane, which can be received and recorded by various detectors.

• Spectral imaging camera

A spectral imaging camera is a detection device that combines optical imaging and spectroscopic technology. It can provide not only spatial information of ground targets but also spectral information. A spectral imaging camera obtains spectral information of ground objects in different bands through a spectroscopic device. It mainly consists of a front-view telescope objective and a spectrometer, acquiring images of the same target in multiple spectral bands on the focal plane.

Gaze + Scan: A Common Imaging Method

Common imaging methods fall into two categories: staring and scanning. Scanning methods are further divided into panoramic, brush-scan, and push-broom types. Panoramic scanning obtains a two-dimensional image of a local area of ​​the target with each exposure. As the camera moves relative to the ground, multiple local images are acquired under the control of the shutter. After stitching, a complete image is obtained. Push-broom and brush-scan cameras require only a one-dimensional detector and optical lenses that provide good image quality only within the linear field of view. The optical system and detector structure are relatively simple. In particular, push-broom imaging does not require mechanical scanning; instead, it utilizes the platform's flight and the Earth's rotation to achieve scanning. A one-dimensional linear array detector can obtain the object's two-dimensional temporal information. In this method, using a two-dimensional detector makes it easier to achieve high-resolution spectral imaging.

Aerospace optical remote sensing technology:  A global "selfie stick"

Most optical remote sensing satellites operate in sun-synchronous orbit (SSO), passing the same location at the same local time each time. This allows for continuous observation of the same location, recording trends in surface changes. This significantly improves the efficiency of natural resource surveys, ecological environment monitoring, urban management, and disaster prevention and mitigation. Furthermore, optical remote sensing satellites can also be used for military reconnaissance, facilitating the rapid and accurate acquisition of enemy deployments and movements; they are a common type of military satellite.

Over the past few decades, aerospace optical remote sensing technology has developed rapidly, becoming an indispensable means for humanity to understand the world, comprehend the relationship between humans and nature, safeguard national security, and promote sustainable development. Today, my country's civilian optical remote sensing satellites have entered the sub-meter level era. It is believed that as the performance and comprehensive application capabilities of remote sensing satellites continue to improve, the trend of integration between optical remote sensing technology and next-generation information technology will become increasingly apparent. The application models of satellite remote sensing will continue to innovate rapidly, propelling people's lives into a new era.