GISdevelopment.net ---> AARS ---> ACRS 1990 ---> Poster Session

18-23 MSP Multi-Spectral Aerial Photography

Kui Zhongyu,
The Research Institue of Surveying and Mapping
National Bareau of Surveying and Mapping; Beitaipinglu 16,100039
Beijing, China

Niu puning
The General Aviation Co. of Chinay


Abstract
Prior to the research project, the multi-spectral photographic cameras used in the world have a small format (mostly 6cm * 6cm, so it is called 6MSP), the 6 MSP could not be used for mapping; the "harmful absorption" of spectral photometry is great so that the image quality is not up to standard; Due to the small format, the processing work is great during flying and later period. This project uses aerial photo gram metric cameras of format 18cm*18cm and 23*23cm which composed multi-spectral camera groups, and the spectral photometry which has no "harmful absorption" is constituted by "cut-off filter----special sensitive film" that enables the for-mat of the multi-spectral aerial photography to increase by 9 times and 14.7 times more than 6MSP, and it allows" one photography-multiple usage" , e.g. the photographs can be used for mapping and for resources investigation and environment monitoring . As there is no "harmful absorption" so the quality of mult-spectral image is higher, and can be used for visual interpretation and also can be input into computer in order to do the objects classification and interpretation and also can be input into computer in order to do the objects classification and interpretation accurately.18-23 MSP is an efficient aerial remote sensing techniques.

Purpose of the Research
Multi-spectral photography (MSP) had been used in aerial photography in 1959, aimed at carrying out the earth resources investigation. The practice for over twenty years was proved that it is a favorable means for the earth resources investigation, with which many problems of agricultural, forest, water conservancy, geology and environmental projection etc. can be solved. According to the incomplete statistics, there are 29 kinds of MSP photographic cameras in the world, the formats of which are about 6cm*6cm. So they are called 6 MSP photographic systems.

The civil air-photography in China can be divided into two categories: i.e. surveying and mapping; and remote sensing. At present, in the surveying and mapping photography the panchromatic and panchro-infrared photography in mainly used. In the remote sensing the color infrared and multi-spectral photography is mainly used. At the present 6 MSP cameras are used for multi-spectral photography, format is small and camera is no cartographic one; so it is not suitable for mapping. In short, the current two kind of photography are not compatible and the two kinds of photography are required to fly once for each in the same area. Therefore not only the flying fee is increased by several times, but also the time of data delivery is postponed.

In recent years, the photographic policy of "one photography-multiple usage" was proposed by the National Bureau of Surveying and Mapping and the Civil Aviation Agency of China in accordance with the requirement of national economy reconstruction. "One photography-multiple usage" should break through the policy of "each goes its own way" e.i. The separation between the cartographic photography and the photography for remote sensing. In contrast, it should enable two kinds of photography to be compatible. To this end, the aero-photogrammetric camera must be used to take the multispectral images. This project aims at multi-spectral photography by using the aero-photogram metric camera, format 18cm*18cm and 23c*23cm, so it is called "18-23MSP".

To solve a series problem of the theory, method, equipment and material of 18-23MSP aerial photography is a central content of the subject to be developed. To establish the new aerial photographic method " one photography-multiple usage" which is compatible for mapping and remote sensing is the purpose of 18-23MSP photography.

The brief indication of 18-23MSP technologies
The method of 18-23 MSP aero-photography can be briefly described as following: to carry out simultaneous photography with three aero-photo gram metric cameras of format 18cm*18cm or 23cm*23cm,one spectral band can be recorded by each camera, and to complete spectral photometry " three filter three film method" is applied . Its band ranges are G500~600n m, R600 ~ 700 m n and IR1 700 ~800 m n respectively, and it can also extend to B400 ~ 500m n and IR2 800~900nm. The interpretation and general analysis can be carried out band by band using the three black and white negatives or photos; otherwise hundreds of multispectral color composites can be obtained by mult-version and multi-spectral composition. All the black and white and color images obtained can be used for the earth resources investigation and environment monitoring. The acquired image can be also input into computer for classification. The original photo or duplicates of band R is applied mapping.

Airplane: An-30
Camera: 3 set AŘA-T3 20 or 3 sets RC-10;
Method of spectral photometry: Three filter three-film method;
Filter: Yellow X C-18, red KC -14, infrared HB-730 and wild C,D,E;
Photo film: (G) 1055, (R) 1065, (IR) and 1075.
Efficient spectral band: 500~600, 600~700, 700~800, can be extended to 400~500 and 800~900(nm)
Format: 18cm*18cm 23cm * 23cm;
Flying height : 4000m ~ 7000m;
Photo scale: 1:20000~1:45000;

Weather requirement: same as the normal photographic requirement;
Lateral and longitudinal overlap: same as the normal photographic requirement, or reduced overlap for resources investigation
Exposure and developing: The contrast coefficient of three films should be consistent as much as Possible, difference among them Dr should be not larger than ±0.15;
The print enlargement of B/W film: According to photogram metric requirement using three kinds of negative.
Color composting: According to the requirement of resources investigation, color composition can be carried out by the negatives or positives or egative -positive of three or two films.

Theoretical basis and the method of Pectral Photometry
  1. The Theoretical Basis

    The physical essence of spectral photography is: Firstly the reflected light energy of photographed objects will be recorded by photographic film band by band with the similar photographic spectral photometry, then in accordance with the linear relation between the original energy of each band, the reflected energy of photographed objects will be reproduced by certain density or color in the process of monochrome printing or color composition. There are two important processes here, one is light energy recording, and another is light energy reappearing. The two processes are inter-related, light recording is a grantee of reproducing, and it is difficult to reappear if the record is not correct. Therefore, how to record light energy is a key problem of 18-23MSP.

    Hereon a discussion of correct recording is given.

    According to the basic relation of photographic sensitivity, the relation between a certain spectral band li acquired from negative and its exposure is :



    H lai and H lbi will be developed and resulted in:



    Where El - The distribution of spectral energy of photograhic light source
    tl - The spectral transparence of photographic filter
    Sl -- The spectral sensivity of film
    ral rbl - The spectral brightness coefficient of objects a,b to be photographed.

    The effective spectral actinic flux A l(Al = E l * t l * S l ) in an aerial photography is a constant, so it can result in :



    The three spesctral bands are used in 18-23MSP e.i, green (G), red (R) and infrared (IR). ON condition that the spectral photometry method assures that there is no light energy interruption among them (called condition I), the green band (G) could have the following relation:





    red band (R) and infrared band (IR) can also have :



    As mentioned above, the linear relation between the original reflected energy of objects to be photographed and their image density on photographed negative must be maintained in multispectral photography so as to benifit the image interpretation . If scale the formulae (1) ; (2), (3) consecutively, it would result in :



    in the formula (4), if g = gG = gR = g IR (called condition 2 ), the formula (4) can be written:



    Formula (5) is the linear relation between the spectral brightness coefficients of objects and their optical densities D on negative in multi-spectral photography can be concluded as below:

    1. In multi-spectral photography, the method of spectral photometry should guarantee that there is no light interruption between each band, e.i, without so-called "harmful absorption" which is common in conventional color photography.

    2. In the process of multi-spectral photography, including the film selection, exposure control and negative developing, a consistent of contrast coefficients of films among all bands should be ensured,
      e.i gG = gR = g IR

    The spectral photometry method of 18-23 MSP photography is decided according to the above two principles.

  2. Spectral Photometry Method

    The present spectral photometry method of mult-spectral photography (6MSP) is that the exposure is carried out on a " multi-spectral film" through a single band filter transmitting different bands, so as to seprate different efficient spectral sensitive sreas. This method can be called " Mult-filter one film method." Most of foreign countries use Kodak film 2424, but our country currently uses multi-spectral films produces in the First Film Factory (Baoding) of Ministry of Chemical Industry. The spectral photometry method of 18-23 MSP is different from the above-described one. As the method in evolves both the purpose of remote sensing investigation and the geometric accuracy of mapping, therefore, the filter installed originally on aerial camera should not be changed as possible to keep the original characteristic of optical system. In order to

    Preserve the geometric accuracy of image and to overcome the weakness of "multi-filter one film method", the 18-23 MSP should not use the original spectral photometry method mechanically, but the method three films with three cut off filters are used. The essence of the method is that the short water fringes will be limited by three cut off filters, at the same time the long wave fringes of the spectral sensitivity will be limited by the respective films. The method can be called "three filter three film method".

    The combination of films and filters of 18-23 MSP is arranged as in following table:

      18 MSP 23 MSP
    Band G R TR G R IR
    Film 1055 1065 1075 105 1065 1075
    Filter XC -18 KC-14 KC-14 HB-730 WILD D WILD E

    In general, "three filter three film method" is able to guarantee the accuracy of light recording and light reappearing in the whole process of multi-spectral photography, it is the fundamental point of 18-23 MSP photographic system distinguished form the other MSP ones.
The geometric accuracy of image
  1. The geometric accuracy for Mapping

    The 18-23 MSP uses conventional aerial cartographic camera, so its geometric accuracy com-pletely meets the requirement of topographic mapping.

  2. The Geometric Accuracy of Color Composition for resources Investigation

    The factors, which affect composition accuracy, are the photographic system error itself and the error caused by composition method.

    The errors of photographic system come from: the synchronism deviation of camera (m1) , the parallel deviation of camera optic axises (m3) as well as focal distance differences and film distorions which can be omitted . While the object's relative height difference is + 500m., the maximum values of these errors, calculated according to precision hotogrammetric formulae for 18 MSP 23 MSP systems are separately expressed as :

      m1 m2 m3
    18 MSP 0.012mm 0.003mm 0.003mm
    23 MSP 0.002mm 0.029mm 0.001mm

    The error is great for optical composition, which comes from the lower accuracy of coidence of points.

    Color composition can be completed by orthoprojector or computer image processing, the image shift between different bands can't be discovered by naked eye's observation.
Application
The techniques have been applied in production tasks of multi-spectral photography for the agriculture, forest, land planning, metallurgy, surveying and mapping, remote sensing and scientific research in more than ten areas, e.g. Dongting lake, Zhuting, Longmen, Hangzhou Bay, Shenzhen, Shenzhen bay, the Yellow River Mounth, Ningxiang, Jiouqnan, Urumqi, Shenmu, Yongxiou and Yueyang . The total Photographic area is 44946.4km2

For the fine quality of image, the blood fluke breeding area was drawn out accurately on 18 MSP image during the environment invitation of Dongting Lake by the techniques. 18-23 MSP uses photographic spectral photometry to separate bands so that the spectral brightness coefficient of object can be measured on acquired image.

18-23 MSP multi-spectral aerial photography is a technology of time-effectiveness, low cost and high quality for photogrammetry and aerial remote sensing as "one photography-multiple usage."

Reference
  1. "The collection of translation for multi-spectral photography". The Information Department of the Changchun research Institute of Optic and Fine Machanics of the Chenese Academy of Science 1977 .11