M. STANLEY SCHLOSSER Spatial Data Systems, Inc.

Goleta, Cali$ 9301 7

Television Scanning Densitometer

Has applications in the field of remote sensing for density slicing.

1 ELEVISION DENSITOMETERS display the gray scale (density) of photographic film as color contours on a color picture tube. The display is instantaneous and provides a quick analysis of many types of remote-sensing photographs.

A typical densitometer, tradename ~ ~ ~ ~ c o ~ o ~ ~ ( F i g u r e I), analyzes the density of photographs from 35 mm up to 9 inches in size into as many as 32 color bands or con- tours. Density accuracy is 0.030 over a 2 0 range.

The geometric resolution is equivalent to a scanning spot llsoo of the height of the scan- ned area, as small as 25pm at maximum mag- nification. This instrument includes an elec- tronic planimeter that allows the measure- ment of the percent area of any one or more of the color bands (Figure 2).

FIG. 1. The Model 704 DATACOLOR is a color tele- vision system for displaying isodensity contours.

Two general classes of remote-sensing photographs are analyzed effectively using the densitometer. First, data from thermal- infrared scanners recorded on film provide pictures in the 8 to 10-prn band. If these thermal pictures are analyzed, the color con- tours can be related to surface temperature and emissivity. Applications include thermal water pollution, ice-pack thickness meas- urements, extent of oil spills, ocean tempera- tures, and ground water distribution.

Second, photographs taken in the visible or near-infrared portion of the spectrum from aerial and satellite cameras indicate certain features as lighter or darker areas. Density slicing using the densitometer displays these features in a highly contrasting color. Fur- thermore, the electronic planimeter allows rapid measurement of the area of the features of interest. Applications include air pollu-

ABSTRACT The use of television scanning densitometers in analyzing thermal scanner and camera photographic data is illustrated by ex- ample. The basic characteristics of the densitometer system include a density range of over two density units displaying as many as 32 colors. A planimeter measures the area of color bands and is used in many applications to assess quickly the extent of the groundfeatures. Techniques and examples include the location and measurement of oil spills, hot water effluent, ground-water distribution, arctic ice, agriculture moisture stress, air pollution, water quality and soil types.

tion, water resource color and quality, and agricultural studies of plant growth, disease, irrigation, and soil studies.

The foliowing paragraphs discuss some of these applications in more detail.

GENERAL APPROACH:

The apparent temperature of the target (ground) is sensed by the detector in the scanner and the detector response is re- corded on film by modulating a light beam to expose the film. Gray-scale film density can then b e related to apparent temperature2. Apparent temperature variations may be due to differences in emissivities of the targets in the field of view as well as variations in abso- lute target temperature. Because tempera- ture differences are detected by the sensor as emitted power differences (a combination of emissivity a n d absolute temperature), a lower emissivity gives the appearance of a colder temperature to the target (ground). For many applications, this is not a problem be- cause the emissivity remains relatively con- stant. For example, thermal pollution dis- tribution and dispersion studies from power plants3 are usually flown over the same body of water, either fresh or salt, so that the emis- sivity is essentially constant. The same is true in the study of ocean temperature, current flow patterns or arctic ice4.

Further, in the monitoring of oil slicks53 6 7

the emissivities ofthe oil and water, although different, are essentially constant. Therefore, variations in the apparent temperatures ofthe oil and water can be related to true tempera- ture variations. Within the oil slick itself, it has been shown that the variation in tempera- ture can b e related to the thickness of the oil on the surface.

I n other applications, such as ground-water distribution and irrigation studies, the abso- lute temperatures are not required. Only the relative variations of temperature are of in- terest to indicate moisture concentrations.

CALIBRATION TECHNIQUE

The reference level from which the appar- ent temperature differences are generated may b e obtained by clamping it to some ref- erence temperature source or by providing an average of the the signal variations over some relatively long-term integration. The analysis of the thermal scanner film on the densitometer yields color contours which represent iso-thermal contours of the scene. These iso-thermal contours can be read quan- titatively by one of several methods:

In certain types of scanners, temperature refl

erences are recorded as calibration marks on the scanner film which relate temperatures to film density for a given emissivity. By adjusting the controls on the densitometer so that each calibra- tion mark is a different color as displayed on the screen, the imagery can be read directly in terms of temperature from the color contours.

Ground-truth measurements oftemperatures are obtained at the time of the survey which can establish the relationship between temperature and density in the film. By displaying the color- contoured image on the densitometer screen and setting one color in the area of one known tem- perature and anothercolor in the areaof another but different known temperature, then the inter- vening color contours can be related to tempera- ture by simply dividing the temperature differ- ence by the number of intervening color con- tours. This is possible because the color steps remain linear withdensityregardless of the den- sity interval that each color represents.

Radiometer data of scanned area is correlated with thermal scanner film to establish the film densityltemperature relationship. The analysis ofthe film on the densitometer in this instance is essentially the same as stated in the previous paragraph. The known temperature areas on the film being supplied by radiometric measure- ments rather than by actual ground measure- ments. I n all instances, for absolute temperature

determination, emissivity of the particular target of interest must b e known. If television densitometry is used for the analysis of ther- mal scanner film it provides an interactive display of very f ine density differences which the viewer can easily recognize. In addition, scanning the film without changing machine settings, the viewer can study subtle trends and changes in the physical charac- teristics of the ground without laborious analysis.

Airborne photographic monitoring pro- vides a cost-effective means of collecting the necessary data for air pollution because many types of pollutants cover large areas of the earth's surface.

The use of Kodak Ektachrome ER 5257 film with Polaroid and blue filter combina- tions in conjunction with low-sun-angle photographs (LSAP)~ yield photographic data pertinent to the concentration, volume, and distribution of the polluted air mass. The re- lationship between relative transmittance of the film for areas of clean air versus polluted air along with nephelometer measurements in the same areas can yield the relationship between concentration of pollutant and film transmittance.

Viewing the film on the television den- sitometer yields color contours of the pol-

TELEVISION SCANNING DENSITOMETER

FIG. 2. The new color keyboard for DATACOLOR Model 703.

luted air mass. The resulting color contours represent ISO-transmittance values which can be related to concentrations. In addition, using the Planimeter, areas and volumes of the polluted air mass can be quickly deter- mined.

In addition to air pollution, television den- sitometry ~ i e l d s an analysis of water qual- ity. Either by using pre-placed ground con- trol reflectances or using the scene color standard techniqueg, the peripheral atmos- pheric and light source effects in the aerial survey process are removed. Accurate value of terrain spectral reflectance may then be obtained using the densitometer. Areas of flooded acreage and polluted water may be quickly measured as in the measurement of air pollution previously described. Another application of densitometry techniques is the detection and measurement of biological stresslo. Many insect and disease attacks cause disruption of the water metabolism of trees by plugging or severing the water and solute conducting tissues. Trees subjected to such attacks become less vigorous and their foliage indicates this condition by the change in light reflectance from normal healthy foliage. Further, it has been established that the emitted temperature of affected trees can be as much as 2OC to 50C warmer than normal trees.

Although the stressed trees can be imaged on infrared line scanners, it is not necessary to use this elaborate a sensor. Good results have been obtained from aircraft using in- frared aerographic film with a Wratten No. 89B filter, exposing in early afternoon when transpiration is near maximum.

The degree of stress can be related to den- sity of the film because the reflectance of the foliage in the scene (for a given sun angle) varies with moisture stress. Therefore, dif- ferences in brightness levels in the imagery indicate normal or stressed trees. The cali- bration of the brightness levels is accomp- lished by obtaining ground-truth measure- ments at various locations. Further, the total area of infected or stressed trees can readily be obtained using the planimeter and the scale of the photograph.

Similar techniques using television den- sitometers have been applied to identifying and mapping soil limitations to land usell. Using infrared film in aerial cameras to map a potentially irrigable area in South Dakota, representative patterns of claypan and topo- graphical soil limitations on bare soil andveg- etated surfaces were photographed. A map of the soil limitation was made by photograph- ing the color encoded representation of the area displayed on the television densitom- eter. The densitometer planimeter measured the area of each soil limitation.

A few of the uses of television scanning densitometers in remote sensing have been outlined. As the photographic emulsion is, and is sure to remain, one of the more useful mediums for the recording of remote-sensing data, many other applications are sure to be found for television densitometers. The tele- vision method yields results with an accuracy commensurable with remote-sensing data and has the advantage of speed and feature enhancement. The future large volume of remote-sensing pictures will make the quick-look capability of television systems indispensable.

1. Technical Brochures on DATACOLOR Model 703, Model 704, Spatial Data Systems, Inc., Goleta, California.

2. Bastuscheck, C. P., "Ground Temperature and Thermal Infrared", Photogrammetric En- gineering, 1970, Vol. 36, No. 10, pp. 1064-1071.

3. "Pollution Detectives", Skyline Magazine, Vol. 28, No. 4, 1970, North American Rockwell, Downey, Califomia.

4. "Automatic Processing of Arctic Pack Ice Data Obtained by Means of Submarine Sonar and Other Remote Sensing Techniques", pub- lished in NATO Paper presented at the AGARDIEPC XVII Annual Symposium in 1971.

5. Estes, John E and Golomb, Berl, Department of Geography, University of California, Santa Barbara, California, "Oil Spills Can be Meas-

ured", Pollution Engineering Magazine, Nov.-Dec. 1970.

6. Estes, John E. and Golomb, Berl, Department of Geography, University of California, Santa Barbara, California, "Monitoring Environmen- tal Pollution", Journal of Remote Sensing", Mar.-Apr. 1970.

7. Estes, John E. and Golomb, Berl, Department of Geography, University of California, Santa Barbara, California, "Oil Spills: Method for Measuring Their Extent on the Sea Surface", Science Magazine, Aug. 1970.

8. Veress, S. A,, "Air Pollution Research", Photogrammetric Engineering, 1970, Vol. 36, No. 8, pp. 840-848.

9. Piech, Kenneth R. and Walker, J. E., Cornell

Aeronautical Laboratory, Inc., Buffalo, N. Y., "Photographic Analyses of Water Resource Color and Quality", presented at the 37th An- nual Meeting of American Society of Photo- grammetry, Mar. 7-12, 1971.

10. Rohde, W. F. and Olson, Jr., C. E., "Detecting Tree Moisture Stress", Photogrammetric En- gineering, 1970, Vol. 36, No. 6, pp. 561-566.

11. Frazee, C. J., Myers, V. I. and Westin, F. C., Remote Sensing Institute, South Dakota State University, Brookings, South Dakota, "Remote Sensing for Detection of Soil Limitations in Ag- ricultural Areas", presented at the Seventh In- ternational Symposium on Remote Sensing of Environment, May 17-21, 1971, at Willow Run Laboratories, University of Michigan.

ASP REMOTE-SENSING SYMPOSIUM DRAWS RECORD ATTENDANCE

HE ASP SYMPOSIUM on Management and T Utilization of Remote Sensing Dataheld at Sioux Falls, S.D., October 29-November 1, 1973, was most favorably received. Hosted by the South Dakota Chapter of the ASP, USGS EROS Data Center, and the Sioux Falls C h a m b e r of Commerce , t h e mult i- disciplinary meeting attracted approximately 600 persons including registrants from Japan, Indonesia, Italy, Mexico, Australia, West Germany, Canada, Soviet Russia and other foreign nations. Twenty-five companies ex- hibited a variety of equipment and services that were related to the symposium.

A warm welcome was accorded all atten- dees by the Holiday Inn Convention Center, as well as by the Mayor and townspeople of Sioux Falls, the Chamber of Commerce, and Governor Kniep of South Dakota.

The symposium began on Monday with tutorial sessions, followed by 60 papers pre- sented during the next three days. Highlights included a luncheon keynote speech by Mr. E . A. Godby, Associate Director of t h e Canada Centre for Remote Sensing, in which he outlined the work being done on the ERTS

program in Canada. The banquet speaker, NASA Astronaut Russell L. Schweickart, de- scribed many interesting experiences of the Skylab crew in space. Other highlights in- cluded tours of the nearby USGS EROS Data

Center, and the Remote Sensing Institute of the University of South Dakota at Brookings.

The papers presented at the symposium covered a wide range of remote sensing sub- jects from the interpretation of ERTS-1 data to policing air pollution problems in Tokyo, Japan. Other papers were concerned with the automatic extraction of data, change detec- tion, management of data, recording systems and sensing requirements data. One evening was set aside for informal discussions includ- ing a session on education, applications and global management of Remote Sensing.

As a result of excellent cooperation by the authors, the symposium editor was able to provide a copy of the 700-page proceedings to all attendees at the time of registration. Copies of the proceedings are available at Society Headquarters at a cost of $7.50 for members of ASP, AIAA, AEEE and AGI, and $12.50 for nonmembers. The interest engen- dered by the symposium resulted in acquir- ing almost 100 new members.

Participation by the American Institute of Aeronautics & Astronautics, the Institute of Electrical and Electronic Engineers, and the American Geological Institute was a major contribution to the success of the symposium.

-Abraham Anson ASP Reporter