The author has identified the following significant results. The digital timber volume prediction system was tested with another test area in the Trinity Alps. The estimated gain in precision was somewhat lower than the estimate for the first test area (35%). A combined interpretation of the two areas was made, yielding an estimated gain of 44%, with high statistical significance. This interpretation was used to calibrate the system for an interpretation of 43 primary sample units distributed over 1600 square miles. Preliminary results indicate that a gain of 35% can be realized over this large area in northern California

Langley, P. G.

English

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EVALUATION OF USEFULNESS OF SKYLAB EREP S-190 AND S-192
IMAGERY IN MULTISTAGE FOREST SURVEYS
EREP INVESTIGATION #473
Period Covered: October 1, 1973 to March 31, 1974
Contract Number: NAS 9-13289
Principal Investigations Management Office
Lyndon B. Johnson Space Center
Technical Monitor: Mr. Clayton Forbes
Principal Investigator:
Philip G. Langley
Earth Satellite Corporation
Progress Report
ti74-21971
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EVALUATION OF USEFULNESS OF SKYLAB EREP S-190 AND S-192
IMAGERY IN MULTISTAGE FOREST SURVEYS
.OVERALL STATUS
Since the last report progress has been made primarily in the
following areas: (a) multi-spectral combining of EREP imagery, (b)
testing of developed interpretation software, and (c) testing of manual
photo interpretation techniques.
With these new developments, our status with respect to the
submitted EREP Investigation #473 milestone plan is as follows:
Subtask 1--coordinate transform program preparation and testing,
has been completed.
Subtask 2--digital interpretation program preparation and testing,
has also been completed.
Subtask 3--the development of sampling techniques has been modified
to the extent that we are not concentrating this effort
in a given time period. Rather, we evaluate the possible
gain for a set of sampling methods throughout our
experimentation with various interpretation techniques
to determine which sampling method is best suited to the
particular interpretation technique.
Subtasks 4 and 5--first-look analyses of SL/2 and RB-57 imagery
have been completed and reported on in the previous progress
reports.
Subtask 6--multi-spectral combining of images is reported on in the
present report.
Subtask 7--the automated interpretation of S-192 tapes with the LARS
system has been deleted. We have found that our problem is
of a unique nature, not very well suited to a treatment
with the LARS system. We are, therefore, putting our
efforts in-the testing of the software system specifically
developed for forest volume prediction.
Subtask 8--the coordinate transfer of sample units to RB-57 and EREP
imagery has been completed.
1
Subtasks 9 and 10--manual and digital image interpretation have been
in progress through the months of February and March and
will continue through April.
Subtasks 11 and 12--will be performed shortly before the due date of
the final report.
A significant result was obtained during the completion of Task 1, the
coordinate transforms for the S-190A and S-192 systems, with the resectioning
of an S-190A image. The 70 mm image was enlarged to a scale of 1:843,526
and transferred to a glass plate on which 34 control points were measured
with a Mann TAPI comparator. The coordinates of these points, and ground
control point coordinates obtained from the Coast and Geodetic survey were
then used in a spatial resectioning program. This program is capable of
doing a classical resection as well as an empirical polynomial adjustment.
The overall RMSE of the resectioning proved to be 106 m on the ground. With
an additional 2nd power polynomial adjustment RMSE's of 100 and 90.2 m were
obtained in the x and y directions, respectively. These results are better
by a magnitude of 2 than those obtained from ERTS, due to a better defined
geometry, the use of SKYBET parameters, and a better ground resolution for
control point identification.
In the following sections we report on the completion of subtasks 2 and
6, digital interpretation system testing and multi-spectral combining of
EREP images.
Testing of the Digital Volume Prediction System
In the previous report we described the testing of the digital timber
volume prediction system on a 64-square-mile test area in Northern California's
2
Trinity Alps. From this systematic experiment with two ERTS MSS bands
from which tone and contrast features were extracted, we initially
estimated that a potential gain of 50% in sampling precision could be
realized by using the digital prediction system. This optimism has been
reduced somewhat for our test area although the gains still appear to be
significant. Testing for the potential gain that may be realized from
EREP S-192 data still needs to be determined.
The first test area contained a water body, which we.thought could
exaggerate the potential gain, as water is naturally associated with zero
timber volume. For this reason we also tested the system on another area
situated further north in the Trinity Alps which contained no waterbodies.
For calibration purposes we again used timber volume estimates obtained
manually from highflight U2 photographs and volume estimates provided by
the Southern Pacific Land Company. We performed the same kind of systematic
experiment as the one for the first test area, but omitted the contrast
factor, as we had found it to be of little significance.
The results for this test area confirmed our previous findings as
far as the ERTS band combinations were concerned, but the estimated potential
gain was somewhat lower at 35%.
The calculated gain percentages were estimates based-on test areas,
and the real performance of the system can best be assessed by predicting
timber volumes over a much larger area, based on the calibration data of
the two test areas. Consequently, calibration coefficients were obtained
by making a combined interpretation of the two test areas (128 square miles).
The estimated potential gain from this combined test area run was 44%.
3
The statistical significance necessary for a useful predictor was more than
twice the required value. Thus, we were confident that statistically
significant results could be obtained outside the test areas.
The next step was to test the performance of the system on a set of
primary units spread over a 1600-square-mile area. The selected primary
units were previous sample units in a timber inventory performed by Earth
Satellite Corporation for the Southern Pacific Land Company. We, therefore,
have accurate and recent timber volume estimates for each unit based on
ground samples and low-altitude aerial photography. Each primary sample
unit may consist of up to 8 one-square-mile land sections. The
following results were obtained for the interpretations made for the
complete set of PSU's.
Table I shows the reduction in the variance of the estimate of total
timber volume and volume per acre that is attributable to digital inter-
pretation of ERTS data or manual interpretation of highflight color
infrared aerial photography, scale 1/120,000 for three types of sampling
plans. In all cases the figures show the gain achieved when the NASA-
furnished data are used in conjunction with EarthSat's estimates
derived from ground data and low-altitude aerial photography.
It is significant to note that the gains are generally higher when
estimating total volume than when estimating volume per acre. The
magnitude of these differences indicates that the size of the area covered
by a particular vegetation class,as interpreted from the space or highflight
imagery, is at least as important as the absolute values obtained from the
signature analyses per se.
4
Table I
REDUCTION IN VARIANCE DUE TO DIGITAL ERTS OR HIGHFLIGHT DATA
(In Percent)
All Primary Units Four Outlyers Removed
N = 41 N = 37
Data Source: Digital Highflight Digital Highflight
Variable Probability
Sampling 44 8 57 12
Total Stratified Sampling 21 17 12 9
Volume
Regression Sampling 49 34 55 31
Variable Probability
Volume Sampling 17 1 17 -43
per Stratified Sampling 6 27 9 64Acre
Regression Sampling 11 9 18 7
The next step in the digital processing phase will be to repeat
the test sequence using data from the EREP S-192 multi-spectral scanner.
Multi-Spectral Combining of EREP Images
We have examined photographic and scanner type images from Skylab
S-190A and S-192 passes #34 and #37 over our northern California test
area. Instruments used during the image analysis were the I2S Addcol
(International Image Systems) and the VP-8 Image Analyzer (Image Systems
International). In this section we describe the techniques used with
each machine, the image materials used, and the results we have obtained
to date.
12S Addcol
The basic technique used with this machine is the use of projected
light through colored optical glass filters for each of four image samples.
5
The samples are selected bands of the multi-spectral coverages of the
S-190A imaging system.
The four image samples (70mm positive transparencies) are viewed
first without filters in concert and registered on a diffuse glass viewing
screen as one composite image. A colored optical filter is then placed
between each of the projection lights and the image samples. The result is
a color composite image on the viewing screen. For enhancement purposes the
light intensity, light position and filter color can be varied for each
image sample. When the desired image is produced on the viewing screen the
image is copied from the screen using a Hasselblad camera and Ektacolor
film. Our experience with the S-190A imagery resulted in the following
combinations of light intensity settings and filter for each image sample:
Sample I 2 S Addcol
Skylab Image Bandwidth p Light Intensity Filter
Roll 1 6900 - 8000 9.1 Red
Roll 2 7700 - 1000 8.7 Red
Roll 5 5800 - 8000 8.5 Green
Roll 6 4700 - 5800 10.0 Blue
The resulting image provides the greatest contrast and enhancement which
could be obtained with the sample images when judged visually. In this
case our objective was to register the existing forest stands in contrast
to non-timbered and barren lands over our test area. This method would
provide us with a level of data input for initial timber volume predictions
over the test site.
The same procedure was used with S-192 images from pass #37. In this
case we had only three image samples which represented the spectral bands
and bandwidths of concern to us in this investigation. Light intensity
6
settings and filter combinations used for each image sample were as
follows:
S-192 I2S Addcol
Skylab Image Bandwidth L Light Intensity Filter
Band 7 .78 - .88 8.7 Green
Band 11 1.55 - 1.75 8.5 Red
Band 2 .46 - .51 7.8 Blue
Our observations of the composite images produced for the S-190A
and S-192 image sample have led usto the following conclusions: (1) In the
case of the S-190 composite image we find that there is a loss of image
quality from combining the images and projecting them onto a ground diffuse
glass viewing screen. Second- or third-generation color infrared trans-
parencies already delivered as a Skylab product are several orders of
magnitude better for interpreting photographic detail; (2) we find that
color enhancement of the several bands via the I2S machine does not produce
equally as good or better color contrasts for forest vegetation over our
test area as does the color infrared film transparencies already delivered
to the investigator. In the case of the S-192 images, the photographic
quality is fair to poor. However, we can make a few comments regarding our
observations of the utility of S-192 as an imaging system.
Band 2 (.46 - .51 p ) has wavelengths too short to be useful in
vegetation analysis. Detail is obscured and feature contrast is almost nil.
Band 7 (.78 - .88/p) would be the best of the three for vegetation
analysis. Detail is clearer and contrasting vegetation features are
interpretable with study of this iamge.
7
Band 11 (1.5 - 17.5 p) seems to produce an image similar to a radar
image of terrain. Geographic features show some contrast, waterbodies
and water courses show sharp contrast and detail. Detail in these features
is readily interpretable, but for vegetation analysis this portion of the
spectrum is not appropriate over our test site in California.
VP-8 Image Analyzer
During this reporting period we have unfortunately experienced many
electrical and other engineering problems with this particular machine.
Consequently we have not been able to finish the experiments anticipated
during this reporting period. In place of reporting results at this time
we can describe the techniques we are using with the VP-8 to obtain data
from the several bands of S-190A imagery.
The VP-8 system utilizes a video camera and two television receivers.
Between the camera and receiver are the electronics which measure the film
density responses of the several bands. The video receivers display the
scene collected by the camera lens. It is possible to make point density
measurements within the images area on the video screen by means of an
electronics cursor which scans a coordinate system built into the video
screen. Any point on the screen can be measured for density and these
measurements repeated via coordinate repetition so long as the image
sample is not moved.
Our measurement technique will be to select a series of nine locations
within each GLO section found on the video screen image of. an S-190A
frame. At each of the nine locations within each section we will measure
8
the film density of that point. This process will be repeated for bands
(Roll #5) 1, 2, 5, and 6 of the S-190A images covering the test area.
These measurements will be tallied for each section per band so that
four variables will be obtained for each band per section. These four
variables can then be used in a regression model. This regression model
will assist in the analysis of the contribution these data make in the
prediction of timber volumes from Skylab images.
EXPECTED ACCOMPLISHMENTS FOR THE NEXT PERIOD
Our expected accomplishments for the next period fall into the
following categories:
1. Completion of the program to ready S-192 digital tapes.
2. Begin the analysis of the S-192 digital timber volume prediction
experiment using a preliminary 5-second burst from Skylab II.
3. Manual interpretation and analysis of RB-57 photography.
4. Manual interpretation of S-190A imagery.
5. Machine-assisted interpretation of S-190A imagery (VP-8
image analyzer).
SIGNIFICANT RESULTS FOR THIS PERIOD
The digital timber volume prediction system was tested with another
test area in the Trinity Alps. The estimated gain in precision was some-
what lower than the estimate for the first test area (35%). A combined
interpretation of the two areas was made, yielding an estimated gain of
44%, with a high statistical significance. This interpretation was used
to calibrate the system for an interpretation of 43 primary sample units
distributed over 1600 square miles. Preliminary results indicate that a
gain of 35% can be realized over this large area in Northern California.
9
The resectioning procedure for our test areas in Trinity County
has been completed for the RB-57 support imagery and the SL-190A
imagery. This step is important to the final analysis of our forest
survey experiments using SL-190 and SL-192 Skylab coverage.
SUMMARY OUTLOOK FOR THE REMAINING EFFORT TO BE PERFORMED
We are still behind in our overall effort with respect to the
milestone plan due to personnel scheduling problems and delays in delivery
of the required data products. We expect to be able to extend our effort
until September 30 with NASA approval.
The overall outlook for the use of space imagery in timber volume
predictions is encouraging, and we expect our current ERTS results to be
confirmed by experimentation with the EREP imagery. The results obtained
so far are statistically significant, and their eventual implementation
is, therefore, a matter of opportunity and economical considerations.
TRAVEL PLANS
None.
10


Evaluation of usefulness of Skylab EREP S-190 and S-192 imagery in multistage forest surveys

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