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offset. This is felt to be a function of different and 
variable mirror scan velocity profiles for the MSS's on 
Landsats 1, 2 and 3 relative to the profile which is 
documented in the Landsat Data Users Handbook (U.S.G.S., 
1979). Recall that the mirror scan on the MSS occurs in a 
west to east direction and can change during the life of 
the mission, whereas satellite velocity in the north to 
south polar orbit is relatively constant during the 
scanning of any given scene. Thus, in general, one can 
expect greater variability to occur in the east/west 
direction. 
When development of the mosaic was initiated, the average 
line and sample residuals were expected to be less than or 
equal to one pixel, with worst case offsets less than or 
equal to three pixels. Using this general overall 
guideline, quadrants 1, 2 and 7 meet these requirements in 
both line and sample directions. Quadrants 3 and 4 meet 
the guidelines in the line direction only. Line residual 
values in quadrants 5 and 8 are only slightly greater than 
desired. The greater than desired offsets in the sample 
direction for quadrants 3, 4, 5, 6 and 8 are felt to be 
caused by the mirror scan differences discussed above. 
The results of the mosaic geodetic accuracy assessment 
indicates that a user cannot expect to accurately cross 
reference points on a map and the mosaic at the single 
pixel level. However, the registration is sufficiently 
accurate to estimate the areal extent and location of 
defoliation by county or forest pest management district. 
Creation of the Remaining Data Layers 
The Landsat scenes selected for the Pennsylvania mosaic 
were the most recent non-defoliated summertime images 
available. These same scenes were used to generate the 
"1/0 forest/non-forest mask" for the State, as described 
under Step 1 of the forest defoliation assessment procedure. 
This statewide forest resource map was then digitally 
registered, image-to-image, to both halves of the mosaic 
and input to the data base. 
Data layers representing the county boundaries and Forest 
Pest Management District boundaries were created by digi 
tizing these features from 1:250,000 scale U.S.G.S. topo 
graphic maps. Figure 4 is a line drawing of the county 
boundaries. This illustration was created using a line 
plotter driven by software which utilized the computer 
compatible tapes created during the digitizing process. 
Additional data layers consisting of MSS data or other map 
registered information can be added as the need arises. 
For example, the registration of 1981 Landsat data 
depicting defoliation conditions is currently being 
completed, so that a thorough test of the automated 
defoliation assessment procedure can be conducted. 
Data Management Front-end System 
The next step in developing the operational system for 
insect damage assessment was the development of a data 
management front-end system that would interface the data 
base with image analysis software. ORSER was requested