WORKING GROUP 6 
POPHAM 
391 
Tiros is an acronym for Television and Infrared Observation Satellite. 
Each of the five tiros satellites launched thus far have carried two cameras, 
two tape recorders, infrared sensors (with the exception of tiros i), horizon 
scanners to provide altitude data, and the necessary clocks, circuits and tele 
metry equipment to provide tracking data and to permit the command and 
interrogation of the vehicle. 
A tiros satellite is a spin-stabilized vehicle, rotating at 12 rpm about an 
axis through the geometric center of the top and base. One camera is mounted 
near the center and one near the outer edge of the base. Both cameras are 
pointed parallel to the spin axis. This is a space-oriented vehicle, i.e., the spin 
axis is directed toward a fixed position on the celestial sphere as the vehicle 
orbits the earth. However, the earth’s magnetic and gravitational fields exert 
a torque on the vehicle which causes the spin axis to precess, moving it through 
one cycle in approximately two months. 
Three different types of cameras have been carried by tiros satellites. A 
wide-angle camera, which views 104 degrees in the diagonal, has been in 
cluded on each of the five vehicles; a narrow-angle camera, viewing approx 
imately 12.7 degrees in the diagonal, was used on tiros i and n; tiros iii 
carried two wide-angle cameras; and a camera lens with a 76 degree field of 
view was used on tiros iv and v. 
When a picture is taken by the satellite, the photosensitive surface of a 
half-inch vidicon tube is exposed for about two milliseconds. The image is 
scanned in two seconds, with 500 scan lines, and is then stored on tape or 
transmitted directly to the ground station. The received signal is converted to 
an image on a kinescope, which is then photographed with a 35 mm camera. 
A film positive is reproduced for use by the meteorologist in preparing the 
nephanalyses, or cloud-depiction charts, which are sent in facsimile to the 
National Weather Satellite Center for distribution on appropriate national 
and international facsimile circuits. 
Tiros i gave the first positive indication that ice could be observed from 
satellites. Tiros ii pictures were especially indicative of the potential in this 
field; the ice pack boundary in the Atlantic Ocean north of Newfoundland 
was observed and identified, and leads and water openings in the ice, as well 
as large ice floes and fields, could also be distinguished. In addition, the 
general and eddy movement of individual floes in the St. Lawrence River 
could be discerned. 
These and similar observations suggested that a more extensive study to 
develop operational interpretation and analysis techniques, and to fulfil 
research needs, should be conducted. Therefore, the United States and Canada 
jointly planned an experiment to obtain visual and photographic observations 
of ice, snow and clouds for comparison with satellite pictures. The first phase 
of this experiment, designated Project tirec (tiros Ice Reconnaissance), began 
when tiros iv was launched on February 8, 1962, and lasted for five days. 
Phase II began April 2, when the attitude of the vehicle was again favorable 
for observing the Canadian east coast waters or the Great Lakes area, with