Our guest today is Jeff Masek, the Landsat 9 Project Scientist for NASA at the Goddard Space Flight Center. Jeff’s role is to ensure the scientific integrity of the Landsat mission. This involves overseeing adherence to a number of project requirements, as well as investigating and testing the performance of the instruments onboard the satellite. He also has the privileged role of reviewing the images that come down from the mission. Jeff has been with NASA for over 20 years, applying his research skills obtained from Haverford College, and Cornell University.
What is the Landsat Mission?
Landsat is the longest running live land remote sensing system in the world. It is responsible for nine satellites which have collected over nine million images of our Earth’s landscape in the past 50 years. A joint mission between NASA and the USGS, Landsat has inspired similar missions abroad, such as the Copernicus Sentinel 2, the European Space Agency’s own project.
Landsat 8, and now Landsat 9, follow a sun-synchronous orbit, chasing the horizon to capture routine coverage of the Earth’s land surfaces every 16 days. If they work in conjunction as a constellation, this timeframe is reduced to full coverage every 8 days. Images are collected at 30x30m resolution, about the size of a baseball diamond.
Although this is not the highest resolution on the market, it serves its audience well for the purpose of monitoring changes in the land due to the regular frequency of collection,
and the general breadth of the archives across the near history of the Earth.
Landsat data is available to the general public via the USGS EarthExplorer interactive map. As a public good, this well-maintained raster data can be accessed by anybody, but it is generally most useful to earth scientists. The open dataset allows monitoring of natural resources, like agricultural fields, forests, and glaciers.
It is difficult to manage what you can’t measure, and thus Landsat data serves as a wonderful tool for more conscientious management of resources. In agriculture, it helps provide insight to crop health and yields, facilitating food security discussions. In forestry, Landsat imagery can be used to measure afforestation and deforestation, as well as to help monitor the effects of diseases or insects.
These two areas in particular are vital for tracking changes related to carbon sinks to better understand impending risks from climate change.
On that note, Landsat data has gained traction in the cryospheric community, allowing researchers to monitor changes in glaciers, ice caps, and other frozen water bodies over time.
How Does Landsat Collect Imagery?
Landsat 8 collects data across 11 bands in the visible light spectrum, near infrared, short wave infrared, and thermal infrared, as well as a panchromatic band. Landsat 8 and 9 use the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS) to fulfill the mission of full coverage every 16 days.
Considering there is a 50 year archive of data collected under the Landsat mission, great care is taken to promote interoperability between missions to avoid leaving any gaps in functionality. In fact, NASA and the USGS communicate with the European Space Agency to encourage standardization wherever possible, such as with ground correction and orthorectification, to create more scientifically viable products for our increasingly globalized research community. This is best achieved by using a common DTM to allow consistency in the supporting geodesic workflows.
Landsat satellites receive what is essentially a to-do list everyday which guides its collection.
In special circumstances, such as natural disasters, the satellite can be tasked and has the ability to roll off nadir to capture adjacent areas of interest.
A satellite can hold about a day’s worth of data at a time. This data is beamed down to ground stations whenever the satellite is within range. There are four primary stations. One is in Alaska, one in Norway, in Australia, and another in Sioux Falls, South Dakota at the EROS data processing center.
These locations are closer to the poles to allow the longest possible communication between the stations and the satellites due to how the orbits line up.
Before the USGS can begin implementing correction algorithms and harmonizing the spectral bands of Landsat products, they must first get the satellite up into orbit. This is where NASA comes in. They are responsible for building, and launching the satellites before turning over the reins to the USGS to collect, distribute and archive the data. It takes anywhere from 5 to 7 years to get a satellite into orbit from the initial inception of the project.
Testing alone can take up to a year. It is necessary to test at the component, instrument, and observatory level to ensure the integrity of the overall mission. These elements are tested in a vacuum chamber to simulate the space environment, as well as the hot and cold extremes, and even electromagnetic and soundwave testing to prove durability.
Considering it is a priority to minimize moving parts in the satellite construction, there are very few of these to worry about.
The true limiting factor to the longevity of a Landsat mission is its fuel.
Due to the slight gravitational pull of the Earth on the satellite while it is in orbit, that orbit will begin to degrade as the satellite is pulled closer. It is necessary to fire the thrusters occasionally to give the station a little push back out into its expected orbit. Landsat 7 has run out of fuel, and drifted close enough to Earth that its data is scientifically unusable. In order to be decommissioned, a reserved amount of fuel will be used to slow it down, and allow it to reenter the Earth’s atmosphere in a controlled and more predictable way to minimize risk to those on the ground.
What Next for Landsat? Landsat NeXt
There are a few challenges that the Landsat mission is looking to tackle in the somewhat near future. As mentioned before, the biggest dictator of mission longevity is fuel supply. This has birthed OSAM-1, a refueling and servicing special project. OSAM-1 would essentially be a robotic arm and a gas can, allowing existing Landsat projects to be revitalized for continued collection.
The wishlist item of current USGS Landsat customers is to have an image available for everyday. Although this target is unrealistic due to budget and resource constraints, it does provide a motivational target for the Landsat mission, especially in collaboration with other projects just as Sentinel. The Landsat mission and the ESA will likely continue to work together more closely in the future to enhance their shared scientific interests.
The most exciting future development of the Landsat program is Landsat NeXt. Landsat NeXt would be capable of collecting 25 spectral bands, creating unprecedented data access for the global community. The project is still in the design phases, but it is expected to be active by 2029. There has been inspiration from the cubesat industry, which means we may see multiple, smaller satellites working together as a constellation in the future.