Ramsey Electronics URC1 Instruction Manual download pdf (Page 4)

WSR-1A• 4

INTRODUCTION TO THE WEATHER SATELLITE RECEIVER

The days of guessing the weather by looking at the clouds overhead have just

ended. Now you can look at the clouds from above! This project will allow you

to receive pictures from satellites 600 km overhead. A typical NOAA satellite

can cover nearly 1/16 of the earth in a single pass! In New York, we are able to

clearly capture images from mid-Hudson bay (where there was still ice in late

spring), all the way down past Cuba, as well as spanning from Wisconsin to far

out in the Atlantic Ocean. The clarity of the image was enough to see the

individual Finger Lakes (in New York), and shadows on the underside of

thunderstorms.

This receiver kit allows you to receive weather satellite transmissions on the

VHF band, where most of the polar-orbiting satellites are located. You will

recognize these transmissions on the news when you see the time lapse of the

clouds darting across the countryside. The weather man in this case has taken

multiple images on the computer, aligned and pieced them together, and then

run through one image after the other. It is possible to do this same thing with

this kit and the proper software.

The way in which a weather satellite works is fairly simple. Just think of your

office fax machine as an example. The satellites circle the Earth going north to

south back to north again almost directly over the poles, which is why they call

it a polar orbit. This means that the satellite will cover every location on the

Earth at least twice per day. With a good antenna, and partly because of

overlap of consecutive orbits, you can conceivably receive the same satellite up

to six times a day! Notice though that the image received from polar orbits will

be upside down on every other pass.

The satellite retrieves the data in a linear fashion, one line at a time using a

scanning radiometer. The scanning radiometer transmits the equivalent of a

single television horizontal line as the satellite circles the earth. The system

uses a series of optics and a motor driven rotating mirror system to receive a

very narrow line of the image of the Earth. Each line is received at a right angle

to the satellite’s orbital track, so as the satellite circles the earth, a line is

received from west to east or east to west depending on the orbit of the

satellite. The total image is received from north to south or south to north

depending on the orbit also, and this motion is what relays the equivalent of the

vertical scan in a television. You can continue receiving this satellite as long as

it is within the line of sight.

Since all of the receivable satellites are similar, we will describe the ones you

will most commonly receive. The NOAA/TIROS satellites, during the first half of

the transmission, send visible light data to the receiver at the same time they

are taking in the view. Meanwhile during the same part of the scan, they are

recording the infrared view. During the second half of the scan, while the

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Ramsey Electronics URC1 Instruction Manual Page 4