census work, particularly for concentrations of 
wildlife such as elk herds, for flocks of migrat- 
ing ducks and geese, and for people (our great- 
est problem species). Photography should be 
more widely used. 
PHOTOGRAPHIC RANGE INVENTORY 
In a paper prepared for the 1968 Remote 
Sensing Symposium, Huddleston and Roberts 
(1968) described the use of photography for 
livestock inventory. In the past, livestock in- 
ventories have been made by ground counts of 
each of a number of sample areas picked from 
aerial photographs. To reduce the number of 
ground surveys, photographic techniques were 
recently developed and tested in the Sacra- 
mento Valley of California. Complete stereo- 
scopic photo coverage (black and white) of the 
sample areas was obtained at a scale of 1:5000. 
At the same time, a subsample was photo- 
graphed in color at a scale of 1:2140, covering 
about 40 percent of the sample area. Photogra- 
phy was limited to morning hours in the 
spring; the green grass provided excellent in- 
terpretation background. Concurrent with the 
photography, ground crews sampled the same 
fields to obtain data on both crops and live- 
stock. 
Prior exploratory work had shown that 
green grass gave better contrast than brown 
grass for counting sheep, and gave reasonable 
contrast for identifying cattle. The time of day 
was also shown to be important. Animals tend 
to be in the open during the early morning and 
early evening hours. Although these are not 
optimum periods for photography due to sun 
angle and poor lighting, it is essential that the 
animals be where they can be seen. Shadows 
may hide an animal, but they are also helpful 
in identification. Likewise, increased accuracy 
in enumeration with stereoscopic coverage was 
well worth the added expense over nonstereo- 
coverage. 
It had further been determined that a scale 
no smaller than 1:5000 was necessary if live- 
stock inventories were to be highly accurate. A 
Wratten 25A filter was used to improve haze 
penetration and to increase contrast. 
Huddleston and Roberts divided their sam- 
ple into a cultivated stratum and a range stra- 
tum. In the cultivated stratum, reliability of 
numbers was somewhat better except where 
clutter from manmade shields (barns, sheds, 
etc.) was present. Tall obstructions effectively 
shielded animals. An inventory of the range 
stratum involves other difficulties. There is 
more background clutter and isolated animals 
may be missed; the ground data are also less 
accurate. The authors state that prior to a suit- 
able survey, some preliminary sampling is nec- 
essary to properly stratify habitat and to ob- 
196 
tain a check of ground truth reliability. For 
wild animals this would be difficult to do; how- 
ever, the next study to be discussed represents 
a situation in which it was accomplished. 
Huddleston and Roberts concluded that more 
efficient techniques and equipment for rapid in- 
terpretation are needed before operational sur- 
veys are undertaken. However, these advan- 
tages make photographic survey worthwhile: 
(1) Access to remote areas is easier; (2) large 
areas can be covered quickly; (3) certain 
biases of ground surveys can be eliminated; 
and (4) the count has greater objectivity. They 
state: 
“It seems likely that the use of aerial 
photography to supplement conventional 
enumeration methods can lead to an im- 
provement in the quality of livestock in- 
ventory statistics. . .,”’ and “The first ef- 
fort to introduce remote sensing into an 
existing data collection system might be 
done most judiciously by incorporating it 
into the quality control or re-enumeration 
phase of the survey.” 
INFRARED SCANNING AND RADAR 
Croon, McCullough, Olson, and Queal (1968) 
tested the use of infrared scanning techniques 
for big-game census on the University of Mich- 
igan George Reserve deer herd. The George 
Reserve, a 2-square-mile area near Ann Arbor, 
Mich. contains a population of white-tailed 
deer estimated by various methods at about 
100 animals. Vegetation on the Reserve in- 
cludes open grassland, hardwoods, and a lim- 
ited area of pine. To extend the test, three deer 
were placed in small pens under different cover 
conditions—open grassland, hardwood canopy, 
and pine canopy. Radiometer (Stoll-Hardy 
screened for infrared) readings made at the 
time of flight showed the temperature of the 
penned deer and their background differed ap- 
proximately 7° C. The authors report that the 
deer in the grassland and oak woodland were 
easily detected on the imagery, but the deer 
penned under the conifer canopy would have 
been missed if its location had not been defi- 
nitely known. 
The equipment used was an imaging in- 
frared scanner, a line-scanning device related 
to the TV camera. It includes three compo- 
nents: A mechanical scanner, a detector, and a 
signal display system. The heart of the instru- 
ment is the detector; in this case, it is sensitive 
to longwave infrared energy. The authors 
point out that the surface characteristics of an 
object control its emissivity of radiation at any 
given temperature, and they define the appar- 
ent temperature as the product of emissivity 
and the actual temperature (in degrees abso- 
bn ee 
