Classification of aerial photography

According to the classification of photo tilt angle (photo tilt angle is the angle formed by the main optical axis of aerial camera and the ground vertical line (main vertical line) passing through the lens center), it can be divided into vertical photography and oblique photography.

When the inclination angle is equal to 0, that is, the main optical axis is perpendicular to the ground (coincides with the main vertical line) and the photosensitive film is parallel to the ground, it is vertical photography. However, due to various reasons in flight, the tilt angle cannot be absolutely equal to 0, and generally it is called vertical photography when the tilt angle is less than 3. A photograph obtained by vertical photography is called a horizontal photograph. In general, the shape of the ground object image in horizontal photos is basically similar to that of the top of the ground object, and the proportion of each part of the photo is also roughly the same. Transverse photos can be used to judge the positional relationship and measure the distance of each target.

If the inclination angle is greater than 3, it is called oblique photography, and the obtained photos are called oblique photos. This kind of photo can be used alone or in combination with the horizontal photo. According to the implementation of photography, it can be divided into single photography, route photography and regional photography.

Monocular photography: photography of a single fixed object is called monocular photography, and generally only one (or a pair of) photos are taken.

Route photography: continuous photography of narrow areas or linear features (railways, highways, etc.) on the ground. ) Along a route, this is called route photography. In order to connect the features of adjacent photos and meet the needs of stereoscopic observation, there needs to be some overlap between adjacent photos, which is called heading overlap. Course overlap should generally reach 60%, at least not less than 53%.

Area photography: continuous photography of a large area along several routes is called area photography. Regional photography requires parallel routes. The course overlap between adjacent photos of the same route is 60-53%. There should also be a certain overlap between the photos of adjacent routes, which is called horizontal overlap, and it should generally be 30- 15%. When taking regional photography, it is usually required that the route is parallel to the latitude, that is, flying in the east-west direction. But sometimes they fly according to the designed route. Due to the inevitable deviation in flight, it is necessary to limit the length of the route. Generally, it is 60- 120 km, so as to ensure no deviation and lead to missed shooting. It can be divided into full-color black-and-white photography, black-and-white infrared photography, color photography, color infrared photography and multispectral photography.

Panchromatic black-and-white photography: photography with panchromatic black-and-white photographic materials. It can be sensitive to all kinds of colored light in visible light band (0.4-0.76 micron), and is an aerial remote sensing material with wide application range and easy collection. For example, aerial photographs taken for measuring the national basic topographic map in China belong to this category.

Black-and-white infrared photography: photography with black-and-white infrared sensitive materials. It can be sensitive to visible light and near infrared light (0.4- 1.3 micron), especially to aquatic vegetation, and the photographed film has high contrast and resolution.

Color photography: Although color photos can feel various colors in the visible light band, they can show the natural color, brightness and depth of objects, so compared with full-color black-and-white photos, the images are clearer and have higher resolution.

Color infrared photography: Although color infrared photography also senses visible light and near infrared band (0.4- 1.3 micron), it turns green light into blue light, red light into green light, and near infrared light into red light. Compared with color film, this color infrared film is quite different in color resolution, lightness and saturation. For example, green plants are green on color film, but red on color infrared film. Because the wavelength of infrared light is longer than that of visible light, it is less affected by the scattering of atmospheric molecules and has strong penetration, so its color infrared film is much brighter.

Multi-spectral photography: Multi-spectral photography is to use the combination of photographic lens and filter to shoot an area at the same time in different bands and obtain different sub-band photos. For example, the commonly used four-band photography can obtain black and white photos with different blue, green, red and near infrared bands at the same time, or synthesize them into color photos; Or the black and white photos in green, red and near infrared bands are combined into false color photos.