Figure 2.1: The ATS-3 satellite (Source: http://rammb.cira.colostate.edu/dev/hillger/geo-wx.htm)


Figure 2.5: A WINDCO terminal, developed between 1971-1972 (http://www.ssec.wisc.edu/mcidas/software/mcidas25_bams.pdf )



Analogue signals were digitised so that different levels of brightness were assigned numerical values and these values were stored on tape. According to this NASA document, one ATS image could use an entire tape reel when digitised (4 reels for colour). Ultimately, seven track 18 inch reels were used, and these could store 70 images (roughly a day and a half's worth of data). It took an estimated 4 hours between image transmission from the satellite to being visible on a terminal on the ground.


Back to Index ESSA Satellites

2. Satellite Meteorology

By the late 1960s, the use of satellites to look at the weather was increasingly common, but the technology itself was still in its infancy, and even by the end of the Apollo era there were still many experiments designed to see if the data from satellites were as reliable as those from traditional ground and atmospheric measurements.

Early satellites were launched with a lifespan of just a few months, and the images were examined on their return to Earth. These included the early Soviet Kosmos satellites as well as American efforts. Advances in communication techniques then allowed signals from an orbiting satellite to be sent back to a receiving station on Earth where they could be translated into photographic images. Although primitive by 2010's standards, the absence of modern circuit board, micro-chips and programming techniques meant that satellite developers crammed a large amount of complex, bulky, interconnected mechanical workings into a relatively small space. Ingenious solutions were arrived at to achieve simple aims, such as using electromagnets that would align with the Earth's magnetic field in order to maintain a satellite's orbital attitude.

There are two basic type of satellite orbit discussed in this work: geostationary and geosynchronous. Geostationary satellites are placed in a position above the Earth that allows them to observe the same features on the ground at all times. Geosynchronous satellites orbit in such a way that they pass over the same place on the ground at the same time each day. They are effectively always following the same path, but the rotation of the earth underneath them means that each time the return to a specific point in their orbit, they are over a different part of the planet.

Images from a number of different types of satellite are examined in this research: ATS, ESSA (and its ITOS and NOAA variations) and NIMBUS.


2.1 ATS Satellites

ATS stands for Application Technology Satellite, and the satellite used in this research is predominantly the ATS-3, with some contributions from ATS-1 (sometimes seen written as ATS-I and ATS-III).

ATS-3 was launched on 05/11/67 (UK date format will be used throughout this document) and its primary aim was to investigate new ideas in satellite photography, meteorology, and communications technologies. 11 experimental functions in total were on board. It was placed in high earth orbit (HEO) at an altitude of 22300 miles in a position above the equator that allowed observation of the American, African and European continents. Although it was launched by NASA, the experiments it ran involved collaboration with a number of other countries, as well as academic institutions and private companies (see here).

The camera used to image the earth was developed by Dr Verner Suomi of the University of Wisconsin-Madison, Space Science and Engineering Centre, and is shown in figure 2.2.


Figure 2.2 – The ATS-3 Multi-colour Spin Scan Cloud Camera system http://library.ssec.wisc.edu/spinscan/images/msscc2.jpg

While in orbit it span at around 120 rpm, and with each spin it scanned a small line of the Earth's surface, each line representing 3.2 km of latitude. On the next spin it scanned a slightly lower latitude, and over 2400 revolutions it would achieve full coverage. It would take roughly 20 minutes to compose an entire image, after which the camera would reset itself and the process would start again. Most of the archives show a single image for each day, but in reality there was a very good record. As will be in seen in a later chapter this can be used to pinpoint the timing of Apollo images very precisely.

The colour image comprised a blue, green and red channel. These three channels worked for just 3 months, after which the red and blue channels ceased to function. Black & white images were still produced until the mid-70s. At the time it revolutionised satellite meteorology. The frequent transmission of images changed high altitude cloud photography from an interesting 'after the fact' image to almost real time imaging, so that meteorologists were able to see weather systems developing and predict more accurately where they were likely to end up. The other experiments on board the satellite allowed cloud movements to be tied in with other observations of other atmospheric conditions, as well as ground based readings, and investment in satellite technology and meteorology increased significantly.

The satellite became the first to photograph the full Earth from space in high quality colour (see figure 2.3), and this led to the first colour time lapse film of the Earth from space (see below).


Figure 2.3: Earth from space, November 1967 (Example source)

The first US sourced high quality full Earth black and white images (and the first satellite images to feature Earth and moon together, although arguably this distinction belongs to Lunar Orbiter 1) were done by ATS-1. The Russians, however, beat them to it in 1967. It has been argued that the first colour image was by a US DODGE satellite, but the quality is not as good as the ATS. The first recorded image of Earth from space is now thought to be from an American launched modified V2 rocket in 1946 (Air Space Magazine), with the first colour image credited to an Aerobee sounding rocket in 1954. This page gives a good account of the first images from space.

The image shown above in figure 2.3 has often been mis-attributed to Apollo, notably Apollo 11 by British newspaper the Daily Mail. A warning to all on the dangers of sloppy and inadequate research.

Interestingly, the satellite does have a direct link with Apollo.

This NASA page reports that it provided television relay for the live Apollo 11 TV broadcasts to Radio Television Caracas, a Venezuelan broadcaster. It is important to note that it served purely as a relay for the TV signal. It took approximately half an hour for the satellites own camera to create a single image and reset itself, it did not have the capacity to broadcast its own images live. It would also not have been possible for Apollo 11 to send a signal direct to the satellite as it would not have been visible. The main TV signal for Apollo 11's moon walk (Extra-Vehicular Activity, or EVA) was received by stations in Australia and transmitted by the communications satellite Intelsat to Houston after which it was relayed to the rest of the world (NASA source, Parkes Observatory).

ATS-3 stored its recorded images on magnetic tape and then broadcast its signal to Earth over VHF frequencies, where they were received on VHF antennae of the type shown in Figure 2.4.

Figure 2.4: VHF antennae used to receive ATS-3 images (Image Source)

This document describes early techniques where each strip would be printed, with characters such as '*','/' and ')' in order used to simulate a grey scale, involving a huge amount of paper.  Kinescope assemblies (A technique for recording TV images directly on still or moving film) were also used to photograph the TV images.

Information could be recorded on tape and analysed later, but the systems were bulky and slow (figure 2.5).