Difference between TM image, SPOT image and aerial image

The so-called remote sensing is to perceive the target from a distance, that is, to detect the physical properties of the target from a distance.

Generalized remote sensing has been extended to the observation of the earth and the observation of extraterrestrial stars.

In a narrow sense, remote sensing refers to receiving electromagnetic wave information from a target from a distance with a detector without contact with the target, and determining the relationship between the attributes of the target and the target through processing and analyzing the information.

2. Classification of remote sensing

1. Classification of remote sensing platforms

(1) Remote sensing of satellites, spaceships, rockets and space shuttles with altitudes greater than 80km.

(2) The height of aerial remote sensing is less than 80km. Planes and balloons

(3) The ground remote sensing platform carries out remote sensing on the ground. Remote sensing vehicles, ships and towers.

2. Classification by remote sensing media

(1) electromagnetic wave remote sensing Remote sensing with electromagnetic wave as information dissemination medium

(2) Acoustic remote sensing: remote sensing with sound waves as information transmission medium.

(3) Force field remote sensing, based on gravity field, magnetic field and electric field.

(4) Seismic wave remote sensing.

3. Classification of remote sensing

Remote sensing platform classification

(1) Remote sensing of satellites, spaceships, rockets and space shuttles with altitudes greater than 80km.

(2) The height of aerial remote sensing is less than 80km. Planes and balloons

(3) The ground remote sensing platform carries out remote sensing on the ground. Remote sensing vehicles, ships and towers.

Classification by radiation source

(1) Passive remote sensing: The detection instrument directly receives and records the electromagnetic waves reflected by the sun or emitted by the ground itself, that is, the electromagnetic waves come from natural radiation sources-the sun or the earth.

(2) Active remote sensing: the artificial electromagnetic radiation source carried by the sensor itself emits electromagnetic waves with certain energy to the ground objects, and then receives the electromagnetic waves reflected by the ground objects.

Classification by imaging mode

(1) photographic remote sensing: optical photographic remote sensing.

(2) Scanning remote sensing: remote sensing of images obtained by scanning.

4. Characteristics of remote sensing technology

1, spatial characteristics (large detection range)-wide field of vision and macro characteristics.

2. Spectral characteristics (rich in information)-the detection band extends from visible light to both sides, which greatly expands the functions of human senses.

3. Time-phase characteristics (short period)-high-speed and periodic repetitive imaging.

4. It is convenient to collect data and is not limited by terrain.

5, economic characteristics-high work efficiency, low cost, one-time imaging, and more benefits.

6, digital processing characteristics-make it and computer technology together, and realize the combination of a variety of information.

5. A complete remote sensing technology system should include the collection, transmission, processing, storage, analysis and interpretation (application) of electromagnetic radiation information of ground objects.

1. Spatial information acquisition system: mainly completes the collection and transmission of remote sensing data.

① Sensor: It is the equipment that collects and records the electromagnetic radiation information of ground objects and sends it to the ground receiving station, and it is the core part of the remote sensing working system.

② Remote sensing platform: equipment loaded with sensors, also called vehicles.

2. Ground receiving and preprocessing system: it mainly completes the receiving, processing, storage, distribution and application development of remote sensing data.

(1) Airborne system-Generally, direct recovery is adopted, that is, information is recorded on film or tape, and the information obtained will be preprocessed when the aircraft returns.

(2) Spaceborne system-Ground system, that is, the original signal received by the ground station of the satellite ground station should be preprocessed and made into image film or computer compatible tape (CCT) for users to use. The preprocessed data must be stored, which is a data database and automatic retrieval system established for the convenience of users.

3. Information analysis application system

It is a variety of technologies used by users to apply remote sensing information for a certain purpose, mainly including remote sensing information selection technology, application processing technology, thematic information extraction technology and so on.

Chapter II Physical Basis of Remote Sensing

1, electromagnetic spectrum

Arranging various electromagnetic waves into a chart according to the size of wavelength (or frequency) is called electromagnetic spectrum. According to the wavelength from short to long, it can be divided into:

2. Atmospheric window

A band with low loss and high transmittance when electromagnetic waves are transmitted in the atmosphere.

3. Spectral characteristics of ground objects

Concept: Spectral characteristics of ground objects refer to electromagnetic wave characteristics (reflection, emission, absorption and transmission) of various ground objects.

Spectral characteristics of ground object reflection: the characteristic that the spectral reflectivity of ground object changes with wavelength.

Reflectance characteristic curve of ground objects: a curve depicting the relationship between spectral reflectance and wavelength of ground objects in rectangular coordinate system.

Factors affecting the reflection spectrum characteristics of ground objects;

1, moisture 2, mineral composition 3, soluble salt content 4, weathering 5, surface structure

6. Season, vegetation coverage 7. Occurrence, slope direction 8. Others: such as time and climate conditions.

4. Reflectance spectrum characteristics of several common ground objects.

1. Plant: A. There is a small reflection peak near 0.55μm (green) of visible light, and there are two obvious absorption bands near 0.45μm (blue) and 0.67μm (red). B. It is a steep slope at 0.7 ~ 0.8 micron, and the reflectivity increases sharply, forming a peak in the near infrared band between 0.8 ~ 1.3 micron, forming a reflection peak. The absorption bands of water are concentrated in 1.45μm, 1.95μm and 2.7μm m. ..

2. Soil: There are no obvious peaks and valleys. The finer the soil, the higher the reflectivity, the higher the organic matter content, the higher the water content and the lower the reflectivity.

3. Water body: the reflection is mainly in the blue-green band, and the absorption in other bands is very strong, and the near infrared absorption is stronger. When the water contains sediment, the reflectivity of visible light band will increase, and the peak value will appear in the yellow-red region. When the water contains chlorophyll, the near infrared band increases obviously.

4. Rock: Different shapes, no uniform law of change. The reflection spectrum curve of rock is influenced by mineral composition, mineral content, weathering degree, water content, particle size, surface smoothness and color.

Chapter III Types and Characteristics of Remote Sensing Images

1, central projection

It is assumed that the ground object projects a beam of projection straight lines, which are focused on the projection plane through the projection center. In aerial photography, the ground scene is the projection object, the lens is the projection center, and the photographic film is the projection surface. Its characteristics are as follows:

① The projection of a point is still a point.

(2) The projection of a straight line is still a straight line. Only when the extension line of a straight line passes through the projection center does the image of a straight line become a point.

(3) The projection of a plane is still a plane, and its image is a straight line only if it passes through the plane of the projection center.

2, color synthesis

True color synthesis: the hue displayed on the image is the same as or similar to the true color of the ground object.

Pseudo-color synthesis: any three bands or three component images produced by processing are displayed in red, green and blue respectively to synthesize color.

3. Color infrared aerial photos

The tone of the image in the photo is inconsistent with the actual ground features. It is obtained by adding a yellow filter to filter out blue light during photography and using color infrared film for photography.

4. At least five Zhang Weixing images.

Landsat Landsat (MSS, TM, ETM sensors). SPOT satellite (HRV sensor). CBERS- 1(CCD, WFI, IRMSS sensors) of China-Pakistan Resources No.1 satellite. IKONOS satellite. Quickbird data

5. Interpretation characteristics of satellite images in each band.

① TM 1 (0.45 ~ 0.52 micron) belongs to the blue light band.

Strong penetration to water body, which is beneficial to the interpretation of shallow water bottom landform; Generally, the reflectivity of ground objects in this band is low, while the reflectivity of snow is the highest, so the boundary between snow and other ground objects in this band image is obvious, with the deepest vegetation, the second water body and the shallowest fresh snow. However, the blue-band image is seriously affected by atmospheric scattering, and sometimes the image will be blurred.

② MSS4 (0.5 ~ 0.6 micron) and TM2 (0.52 ~ 0.6 micron) belong to the green belt.

It has a certain perspective on the water body, and it can reflect the depth of tens of meters in clear waters, which is beneficial to observe the underwater topography and plays a great role in coastal zone investigation.

The reflectance of vegetation in this band is relatively peak, and the distribution range and growth density of vegetation can be easily distinguished on the image, which can be used to investigate forestry data and grassland distribution.

There is also a good reflection on water pollution (especially pollution).

There is obvious reflection (light color) on lighter stratum lithology and Quaternary loose sediments, urban residential areas, roads and quarries on land.

③ mss5 (0.6 ~ 0.7 micron) and tm3 (0.63 ~ 0.69 micron) belong to the red light band.

It has a certain perspective ability to the water body, which is beneficial to reflect the turbidity of the water body and the flow direction of sediment.

Various rocks (sedimentary rocks, magmatic rocks, metamorphic rocks) are quite different in this band, and the images in this band can better reflect the geomorphological characteristics, which is conducive to the interpretation of geological landforms.

Healthy plants and diseased plants can be distinguished. In this band, healthy vegetation has low reflectivity and dark hue, while diseased vegetation has high reflectivity and light hue.

④ MSS 6 (0.7 ~ 0.8 μ m), MSS 7 (0.8 ~ 1. 1 μ m) and TM4 (0.76 ~ 0.9 μ m) belong to crimson-near infrared.

The effects of these bands are similar, and they are all stages of strong absorption by water and strong reflection by vegetation.

Sensitive to water and wetlands, the land-water boundary is clear, which is conducive to the investigation of water distribution, coastline contour, soil water content and shallow groundwater.

It has a good reflection on the geological bodies related to water bodies in plain areas. For example, the water-filled faults are black and light black line segments, and the hidden uplift and depression are annular belts composed of shallow and deep. In addition, it is also helpful to study the petroleum structure, Quaternary sediment types and the division of old and new diluvial fans in plain areas.

It is sensitive to vegetation reflection, easy to delineate the distribution range of vegetation, able to distinguish trees, crops and grasslands, and has a good investigation of pests and diseases. Healthy vegetation has a strong reflection in the near infrared band, which is a bright light tone, while diseased vegetation is a dark tone.

Generally speaking, the images of MSS7 and TM4 are clear and stereoscopic, which can clearly show the details of various ground objects.

⑤ Tm5 (1.55 ~ 1.75μ m) belongs to the near infrared band.

It is mainly used to detect the water content of ground objects, investigate the vegetation growth of soil water (plant water content), and classify rocks in geological survey (the reflection peaks of many rocks are in this band). And can distinguish snow from clouds, snow is deeper than clouds.

⑥ TM7 (2.08 ~ 2.35 microns) belongs to the near infrared band.

This is specially designed at the request of geologists.

It is mainly used to detect rock types, which is beneficial to the study of clay minerals, carbonate minerals and their lithology (dark tone). This is beneficial to regional geological mapping and the study of large-scale alteration zone.

On the TM7 image, the water body is black, and the images of other objects are similar to those of visible light.

⑦ mss8 (10.4 ~ 12.6 micron) and tm6 (10.4 ~ 12.5 micron) belong to the thermal infrared band.

This band records the thermal radiation information of the ground object itself. Provide temperature field data of thermal display. Detect minerals related to thermal anomalies, such as oil and gas, coal, uranium, oxidation zone of sulfide deposits, and detect geothermal and forest fires (3 ~ 5 microns).

6. Four resolutions

Spatial resolution: refers to the size of the ground range expressed in pixels, that is, the instantaneous field of view of the scanner, or the smallest unit that the ground object can distinguish.

Spectral resolution: the minimum wavelength interval that a sensor can resolve. The smaller the interval, the higher the spectral resolution.

Radiation resolution: refers to the minimum radiation difference that can be resolved when the sensor receives spectral signals. It is represented by the radiation quantization level of each pixel.

Time resolution: refers to the time interval of remote sensing sampling in the same place, that is, sampling time frequency, also known as revisit period.

7. Pixels

It is the smallest unit that constitutes a digital image. In remote sensing data acquisition such as scanning imaging, it is the smallest unit for sensors to scan and sample ground scenes.

8, instantaneous field of view angle

The space solid angle from the satellite to this minimum area is called instantaneous field of view. The spatial resolution of a satellite is related to its height. The higher the height of the satellite, the lower the resolution, and it is related to the angle of view of the satellite. The more inclined the viewing angle, the larger the viewing area and the worse the resolution.

9. Real aperture side-looking radar

RAR directly records the echo signals of ground objects on the moving photographic film. The azimuth resolution can be changed by increasing the antenna length installed on the platform (airplane) and shortening the working wavelength. The disadvantage is that the resolution deteriorates rapidly with the increase of distance.

10, synthetic aperture side-looking radar

Synthetic aperture is synthesized by using the forward movement of the platform, taking the actual antenna as an independent transceiver unit in the antenna array and storing radar echo signals specially. SAR can obtain long-distance high-resolution images without increasing the antenna length, but its equipment is complex and expensive, which requires complex signal processing technology.