Paper | 4 ESIAC: A DATA PRODUCTS SYSTEM FOR ERTS IMAGERY (Time-lapse Viewing and Measuring) William E. Evans and Sidney M. Serebreny, Stanford Research Institute, Menlo Park, California ABSTRACT An Electronic Satellite Image Analysis Console (ESIAC) has been developed for visual analysis and objective measurement of Earth Resources Imagery. The system is being employed to process imagery for use by USGS investigators in several different disciplines studying dynamic hydrologic conditions. The ESIAC provides facilities for storing registered image sequences in a magnetic video disc memory for subsequent recall, enhancement, and animated display in monochrome or color. The unique feature of the system is the capability to time-lapse the ERTS imagery and/or analytic displays of the imagery. Data products have included quantitative measurements of distances and areas, brightness profiles, and movie loops of selected themes. The applications of these data products are identified and include such diverse problem areas as measurement of snowfield extent, sediment plumes from estuary discharge, playa inventory, phreatophyte and other vegetation changes. A short movie is presented to demonstrate some uses of time lapse presentation that have been employed in these investigations. A comparative ranking of the electronic system in terms of accuracy, cost effectiveness and data output shows it to be a viable means of data analysis. INTRODUCTION This article presents some of the information products and their applications to earth resources investigators that have been obtained at SRI as a participant in the NASA ERTS-1 investigations (Contract NAS 521841. Under this contract SRI is providing support to the U.S. Department of Interior, Geological Survey (Water Resources Division) program in Dynamic Hydrology, which is comprised of a number of highly diverse disciplines and areas of interest (see Figure 1). The SRI role in this program is to: provide information on dynamic hydrologic phenomena of interest determine requirements and costs for future on-site electronic data processing. The goal of SRI's participation is to develop methods of dynamic information extraction and processing that might be common to all ERTS investigators, with emphasis on the use of image time-lapse sequence and electronic multi-spectral image change detection procedures. In the pursuit of these purposes SRI has had an on-going development program over the past two years of an interactive system called Electronic Satellite Image Analysis Console (ESIAC) for information retrieval and data processing from ERTS data. A recent photograph of the ESIAC is shown as Figure 2. * In brief, the basic objective of the ESIAC system is twofold: То enhance or delineate the phenomena of interest and extract quantitative measurement of it. Experience under this contract has indicated that, on occasion, the display function alone can contribute enough to understanding of the phenomena that no more output information is required, but in the vast majority of cases there was a need for the second function that of extracting quantitative measurements from the imagery. - ESIAC CAPABILITIES - ESIAC provides an operator/analyst with a means for scanning the imagery and placing selected portions of it in temporary storage for detailed review, enhancement, and analysis. The principal image enhancement technique in the ESIAC is rapid sequential presentation of registered images time lapse series, flicker comparisons, and the like. Additional image enhancement capability is provided through contrast and polarity manipulation, easy scale changes (zoom), and false color display of multispectral imagery. The storage memory is a 16-inch analog magnetic video disc recorder fitted with two moving head channels; each channel capable of storing up to 300 addressable 525-line television frames. Quantitative measurements of distances, areas, and signal amplitues are made under operator guidance and may be output in digital form. *Wm. E. Evans and Sidney M. Serebreny, Analysis of ERTS Image Using Special Electronic Viewing/Measuring Equipment; Proceedings of Symposium on Significant Results Obtained From the Earth Resources Technology Satellite, NASA/GSFC, Volume 1, Part B, pp. 1211-1218, March 5-9, 1973. Recently, three important new capabilities were achieved through additions to ESIAC circuitry: Two Dimensional Color Space Display This display is an oscilloscope with matched wideband x and y deflection amplifiers, connected as shown in Figure 3. This arrangement provides a dynamic version of the two-dimensional diagram frequently used for studying two-band radiometric data. It is particularly useful for (a) identifying amplitude and spectral characteristics of "training" regions in ERTS data, and (b) adjusting the various thresholding, slicing, and ratioing controls to make thematic extractions. a While any two synchronous video signals can be so displayed, typical situation is for the ESIAC to be used to display a time lapse sequence of additive pseudo-color images derived from two different MSS channels. A particularly useful combination for many analysis tasks is to display on the color monitor one of the infrared images (MSS 6 or MSS 7) in red and one of the visible images (MSS 4 and MSS 5) in the complementary color, cyan. While normal TV display is being scanned in conventional rectangular raster fashion, the spot on the x-y oscilloscope is being continuously positioned in accordance with the instantaneous responses in the two image channels being studied. (We refer to the normal TV display as the "image space display" and to the x-y oscilloscope display as the "color space display".) All points in the image which generate equal responses in the two channels will be distributed ("mapped") along a 45° diagonal line in the x-y color space display. Zero response for both channels defines the origin in the lower left corner. In one mode of operation, the brightness distribution over the color space display provides a measure of the color or energy distribution for the entire image; that is, two-band video information is converted into a two dimensional scatter diagram. Scenes containing significant areas of snow or clouds, for example, produce maps showing appreciable energy distributed along the "neutral" diagonal. A heavily vegetated scene on the other hand, will generate a scatter diagram ("map") with most of its energy above and to the left of the diagonal (see Figure 4). Water bodies normally map into the lower right region. By providing intensification (z axis modulation) to the color map display only during the cursor-intersection period, any designated portion of the ERTS image becomes identifiable on the color map and its color coordinates (percent response in each of the two channels) can be read (Figure 5). Leaving the cursor positioned over a vegetated area while cycling through a long sequence of registered images provides a rapid and dramatic portrayal of the changing spectral responses of the vegetation patch as its proceeds through its seasonal changes. Grey-scale storage during vertical retrace The ability to store a calibration greyscale step tablet on the same video disc track as the main image permits the storing of the greyscale and annotation block from an ERTS frame during vertical retrace period of the television signal. This results in a valuable saving in recording capacity on the magnetic disc. Further, when the main image area is being used to display a magnified (zoomed in) segment from a full ERTS frame, the pertinent radiometric calibration data for the frame at zero zoom is still available (by "rolling" the image vertically to display the normal vertical blanking interval). Any gain, dc offset, or amplitude comparison experienced by the main signal during the storage and reproduction process is also experienced by the calibration waveform. The desired effect of having the reference data show at 0°, 45° and 900 on the color space display is achieved by recording the two grey scales slightly misregistered in the vertical direction. Because of the intentional misregister, there will be a brief period (several scan lines) during which only the Band 6 grey scale will be scanned, another brief period during which only the Band 5 grey scale will be scanned, and a third brief period during which both grey scales are scanned simultaneously. It is during this latter period that a color image space display will show a neutral grey scale, and the 45o diagonal line will be generated on the x-y (color space) display. By reading the x and y coordinates of an area relative to the axial dots generated by steps on the film grey scale tablet (interpolating when necessary), two-band radiometric values for the area can be specified in terms of absolute values; e.g., in Watts-Meter-2-Steradian ̄1, with a minimum error due to amplitude non-linearities in the photographic and TV processing steps. Semiconductor binary memory (scratchpad memory) This equipment provides editing and storage of single frames of binary imagery (thematic masks). The additional memory capacity frees both disc channels for use as the data source for time-lapsed color displays, as well as overcoming an annoying operating restriction that previously existed. Some examples of binary thematic masks that can be generated are shown in Figures 6-8. All of these highly interactive additions to the ESIAC analysis capability should be of significant help to investigators interested |