Perhaps the first image that comes to mind when you think of a satellite is that of a huge, heavy device made of sophisticated materials. But not all of them are like that.
They range in size from a Rubik’s cube to the size of a bus, and can orbit the planet because they are catapulted on trajectories that are fast enough to overcome gravity (at least for a while). A satellite starts operating when a rocket carries it into space and, once the determined location is reached, releases the satellite into orbit.
According to the United Nations Office for Outer Space Affairs (UNOOSA) Index of Objects Launched into Outer Space, there are 4,921 satellites currently orbiting.
What is the function of satellites in orbit?
Orbiting satellites around the Earth perform multiple functions including:
- Communications (we see this in the coverage and data transfer of our devices).
- Earth observation, navigation and positioning (the well-known GPS system).
- Space and planetary studies(vegetation, climatic phenomena, thermal mapping, maximum vegetation peaks, carbon levels, etc).
Satellites for environmental purposes
Satellite technology is also a great ally in the study of the Earth and its phenomena. Through remote sensing sensors it is possible to collect data and capture images invisible to the human eye, which can be used to analyze and understand the importance of the balance of ecosystems and help mitigate the environmental crisis.
We created a short list of satellites that have been key to the analysis and understanding of our planet:
The Terra
The Terra satellite was launched into orbit by NASA in 1999. It was the first of the Earth Observing System (EOS) program and its objective was to perform the first complete health check of the planet Earth, in particular, the study of the functioning of the carbon and energy cycles.
Terra has four sensors that measure specific aspects such as:
- ASTER: used to obtain detailed maps of the Earth’s surface temperature, reflectance and elevation.
- CERES: Measures the Earth’s global radiation balance and also provides data on cloud properties and their role in the radiation fluxes from the Earth’s surface to the upper atmosphere.
- MISR: Scans the Earth’s surface with nine cameras, each pointed at a different viewing angle to distinguish different types of clouds and land surface cover. Its images make it possible to see the invisible in four bands: blue, green, red, and near infrared.
- MODIS: Scans every point on the planet every 1–2 days in 36 spectral bands. Thanks to this broad capture capability, this sensor senses more of the Earth’s vital signs than other sensors on the same satellite. Among other things, MODIS measures every day the percentage of the Earth’s surface covered by clouds and detects emissions from fires.
- MOPITT: Captures data from the troposphere and observes its interaction with the marine and terrestrial biosphere. MOPITT data will be used to study the distribution, transport and sources of carbon monoxide and methane in the troposphere.
Landsat 8
The Landsat mission offers different satellite images at different times and resolutions. From Landsat 1 to 8, instruments such as Multispectral Scanner Sensor (MSS), Thematic Mapping (TM), Enhanced Thematic Mapping Plus, (ETM+), Operational Land Imaging (OLI) and Thermal Infrared Sensor (TIS) are available in summary, these instruments allow the following:
- Coastal and aerosol survey
- Bathymetric mapping, which distinguishes soil from vegetation and deciduous from coniferous vegetations.
- Highlights peaks of maximum vegetation, which are useful for assessing plant vigor
- Distinguishes vegetation slopes
- Highlights biomass content and shorelines
- Distinguishes soil and vegetation moisture
- Improved soil moisture and vegetation reading and penetration through thin clouds
- 15-meter resolution, sharper image definition
- Improved detection of cirrus cloud contamination
- 100 meter resolution, thermal mapping and soil moisture estimates
The EO-1
The last of the list is the first satellite of NASA’s Earth observation program for the new millennium. Launched on November 21, 2000, it is the continuation of the Landsat missions.
The EO-1 satellite has three remote sensing sensors:
- ALI: Land Imager.
- Hyperion: It is the first satellite hyperspectral sensor. It captures the colors of the images of the Earth’s surface without leaving uncovered areas, it has the ability to discriminate images, such as the difference between pine and cedar trees.
- LEISA/AC: It is a set of technologies that captures hyperspectral images. As images transmitted by satellites are distorted by gases in the atmosphere, the AC (atmospheric corrector) restores the images to their original form.
What happens when a satellite completes its life cycle?
Once a satellite has served its purpose, it begins to lose altitude and fall. Generally, most end up disintegrating in the atmosphere; others, usually farther away from the atmosphere, are taken to another orbit.
Depending on how close to the atmosphere the satellite is located, its lifetime can be up to 15 years according to international agreements, with the exception of extraordinary cases such as the Hubble telescope, which was launched in 1990 and is still in orbit.
Who can launch a satellite?
At present, everyone. It is not a simple process, nor is it cheap, but it is a possibility that has been opening up to the public in recent years.
“Generally, companies that launch a satellite hire another company to help them with monitoring and data management. They provide ongoing operational support and take the satellite out of orbit at the end of its life cycle,” says Zachary Cohen, Strategy Associate at Odd Industries.
What about people’s privacy and satellite surveillance?
The resolution of the images that satellites can capture ranges, for the most part, from 5 to 30 meters from an orbit of 400km altitude, meaning that each pixel in the image measures 5x5m.
This means that the resolution of most satellites cannot identify people or animals of smaller or similar size (you would have to be a person of more than 25 m2 to be distinguished by the satellite as anything more than a pixel!).
However, there are some satellites with resolutions of less than 30cm (usually for military purposes), so the responsible, ethical and informed use of these technologies is critical for people’s privacy.
If you are interested in learning more about the ethical and responsible use of satellites, and how they can help to understand, analyze, and revert environmental crises, we invite you to sign up for Lemu’s early access and be among the first to hear about environmental solutions and news by logging on to Le.mu.
