From Internet browsing to navigating on roads with GPS, all depends on satellites. What is there on satellites which makes our lives easy? All satellites flown into the space are not same, they differ in size, position, speed and functions. They all are developed and constructed according to the requirements. They are like instruments and appliances meant for a specific use. Lets look into the few famous, crucial and life changing equipments launched into space up till now.
The First Artificial Satellite into Earth's Orbit.
Sputnik 1 - 1957
Sputnik I, it was the first artificial satellite launched by Russia, obviously it was not intended to stay in the space for too long, hence no crucial instruments were installed on it. the satellite was just an aluminium sphere with couple of small radio transmitters and batteries which could send beep beep signals to earth. The signals helped to understand how radio waves travels in ionosphere. drifting and acceleration of the satellite gave details of gravitational effects up in the space.
Sputnik 2 - 1957
sputnik 2 was the first satellite to take a living being along with it. A dog named Laika was kept in a small chamber and was watched by a video signal for up to three days in the space till the dog died on the forth day. Spectrometers were also installed on this satellite to analyse sun-light, x-rays and cosmic rays.
Hubble Telescope 1990
There is a wide range of electromagnetic wave spectrum coming to us from all over the universe, but earth's atmosphere either absorb or reflect back most of the infra-red and ultra-violet radiation back. Mostly visible spectrum of waves are only allowed by earth's atmosphere, therefore the telescopes on earth surface cannot detect objects emitting ultra-violet and infra-red waves.
Only solution to this limitation was to install a telescope outside the earth's atmosphere. Hubble Telescope as its name suggests is actual a reflecting telescope in the space. It is one of the most famous satellites placed into orbit around the globe.
One of the main components of this telescope is a 2.4 meter wide 'concave parabolic mirror' which converge parallel rays coming in from cosmos and direct them to a secondary 12 inch (1 feet) wide 'hyperbolic convex mirror', which extends and divert the focal point of the reflected behind the primary mirror.
Apart from mirrors this satellite has spectrographs which classify different light waves and direct them towards relevant cameras and other devices which could capture the images.
Another stunning device on the board is set of three sensors which keep face of the primary mirror locked towards the target site in the sky. These sensors are so precise that it can target center of small coin 400 miles away, to achieve this while orbiting around the globe in 96 minutes is definitely a rocket science.
GPS is a group of satellites functioning in coordination with each other, sending signals to the highest number of receivers distributed all over the globe. When the first satellite (sputnik-I) was launched, it sent radio waves to earth, by which the station on earth estimated the position of the satellite in orbit. In this group of satellites, the scenario is different. Satellites send radio signals to receivers on earth to locate the exact position of the receiver on the planet.
The essential instruments onboard all the satellites are atomic clocks, and slightly less precise atomic-clocks are present on receivers also. These clocks can measure even 100 millionth of a second. which is achieved by calculating the vibrations of atomic and sub-atomic particles of special elements.
How these clocks help to determine the position of a device is a very interesting technology. If we calculate the travel time of any object with a constant speed between two points, we could find the distance between the points. Electromagnetic waves have a constant speed in any vacuum, these waves include visible light, radio waves, and many others.
The speed of radio waves is so enormous, that it doesn't take barely a tenth of a second to reach receivers on earth from satellites 38000 km away! The exact position of the receiver on earth is calculated with the help of at least 4 satellites in space. The difference in traveling time taken by radio waves from these satellites determines the exact position of the receiver. Hence achieving an accuracy of even 5 meters in the position of the receiver, clocks should be in sync with each other and should be able to measure 100 millionths of a second.
Landsat satellites; series of satellited from Landsat-1 to Landsat-8
Weather forecasting and locating places on the globe need large real images of the Earth. This could only be possible by taking photographs far away from earth with very high-resolution cameras. Landsat Satellites are doing this job for us continuously.
After the first satellite; sat-1 seven successive satellites were launched within 5 decades. Few of them are now not operational. They all are scanning the earth continuously and taking photographs. Like a Camera, Landsat captures reflected radiation from the globe but unlike a normal camera, Landsat operates on many different types of radiation; ultraviolet, visible, near-infrared, and far-infrared.
- RBV-Return Beam Vidicon
- MSS Multispectral Scanner
- (ETM+) Enhanced Thematic Mapper Plus
- OLI Operational Land Imager
These are the main cameras onboard these eight satellites. The specialty of these cameras is that they can also detect non-visible radiation from the earth, especially infrared. pictures taken on these bands are useful to study climate change and the agricultural behavior of humans and society.
Spectral Remote Sensing
Landsat 8 Features
Carbon Mapper by 'Planet'
Like Landsat, Carbon Mapper is also a constellation of satellites going to be launched in 2023. They will scan the earth with a 'hyperspectral scanner'. which means that these satellites will take photographs in all necessary bands with narrow bandwidths (high band resolution compared to Landsat).
The difference in Multispectral (Landsat) & Hyperspectral (Carbon Mapper)
Landsat is having 8 or 9 sensors for each pixel to detect particular bands (UV, visible, near & far infrared) radiation. Carbon Mapper will have hyperspectral cameras which will have around 200 different sensors for each pixel. it doesn't mean that they will detect other extra bands of radiation. Sensors on the hyperspectral camera will have sensitivity for very specific narrow bandwidth in the same band.
Understanding The Difference With an Example
Landsat is having a sensor 'PLANTATION' that detects any wavelength between 400 to 500 on another hand the Carbon Mapper will have ten different sensors (PL-one to PL-ten) for the same 400 to 500 wavelengths but each detects 10 different parts of the same band or range. This makes a big difference.
Suppose leaves of every plant reflect wavelengths between 400 to 500 and every plant has its unique wavelength depending upon substances present in their leaves. Let us say maize leaves may reflect 485 and wheat plant leaves may reflect 405. Landsat will detect both leaves by its sensor PLANTATION and Carbon Mapper will detect maize leaves by PL-eight and wheat leaves by PL-one. This specific detection will help in detecting specific substances on the earth.
What Will Carbon Mapper Detect?
As mentioned above hyperspectral imaging helps in detecting specific substances as each substance has its own unique reflective spectrum. The main objective of Carbon Mapper would be to detect greenhouse gases and substances on earth. The main substances which it looks for would be carbon dioxide, methane, and chlorofluorocarbons. Detecting them would help humans finding out which are the major sources of these gases on earth what could be done to shut them down.