How Do Landsat Satellites Collect And Analyze Data To Map Earth's Surface

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Landsat: the Cornerstone of Global Land Imaging

Advancing the Agreement of Planet Earth

The utilise of data from Landsat satellites has become a cornerstone of global land imaging with wide societal benefits. More real-time monitoring capability in the hereafter will further our understanding of a irresolute Earth.

The Landsat satellites provide an uninterrupted space-based data record of the Earth'south land surface to assist advance scientific research towards agreement our changing planet. In this article, the authors expect at how the use of data from Landsat satellites has evolved over time to become a cornerstone of global country imaging with broad societal benefits. They conclude that the Landsat annal is poised to shift into a more than real-time monitoring capability to help further our understanding of a changing Earth.

Since 1972, the Landsat satellites have provided an uninterrupted space-based data record of the World's land surface to help advance scientific enquiry towards agreement our changing planet. Early Landsat satellites generated a wealth of new information that improved mapping of remote areas and geological features forth with digital analysis of vegetation. Landsat's spatial and spectral resolutions have advanced its use for broader societal benefits such as global crop forecasting, woods monitoring, water use, carbon assessments and as the ground for Google Maps. Landsat'southward long-term data record provides an unrivalled resource for observing state cover and land-use change over a time scale of decades. The free and open up Landsat information policy announced in 2008 unleashed global-level enquiry without the onus of data cost, while evolving analytical and computing capabilities make it possible to tackle complex world issues in search of a solution.

A Revolutionary New View of Our Planet

In the early 1970s, the environmental motion ushered in a new awareness of our planet. The convergence of this movement and the Landsat programme was propitious. The Globe Resource Technology Satellite (ERTS), later named Landsat 1, was a proof-of-concept experiment to demonstrate that infinite-based remote sensing data could better the management of our environment and natural resources. The USA would use the applied experience and evidence gathered from these early on instruments to decide whether to pursue an operational state remote sensing programme .

Multispectral scanner organisation (MSS) data provides improved spatial resolution resolving more land features than were possible with previous Globe observing satellites like the Tv set and Infrared Ascertainment Satellite (TIROS) weather satellite, and besides capture in secondsfield-of-view that would require days to survey past air. April 1960 TIROS-ane image (left) compared to Landsat i MSS image (right) from March 1973. Prototype courtesy: NOAA (left) and USGS EROS (right)

Re-charting the Planet

More than half of the Globe had withal to exist accurately mapped at the time of Landsat one'south launch in 1972. From the offset downloads of data, many revelations appeared in the synoptic view provided past Landsat. Based on these revelations, ane,200 miles of Antarctic coastline were redrawn, navigation charts were improved, a baseline map of the globe's glaciers was created and the positions and courses of many Amazon tributaries were amended. The echo coverage of remote regions also helped to map sea ice to help shipping navigation routes around the Chill. Landsat's medium resolution and large field-of-view made it easier for scientists to discern geological lineaments and identify mistake lines in remote locations, the latter of which fabricated contributions to the and then nascent theory of plate tectonics.

Realizing Societal Benefits

Applied applications held the well-nigh hope for social and fiscal benefits from Landsat data. Satellite data is a relatively low-toll culling to aerial surveys, offering the potential to survey large areas for applications such equally crop reporting, range management, woods management and soil surveying. Inside Landsat'southward get-go year, catastrophic flooding occurred along the Mississippi and Missouri rivers. Landsat information was used to map the extent of areas inundated by floodwaters. When the aforementioned areas flooded again in 1975, the The states Geological Survey (USGS) Earth Resources Observation and Science (EROS) Heart used the rapidly relayed satellite data from NASA to create a overflowing damage map to aid support the case for disaster relief funds.

Early Landsat imagery exposed many errors in contemporary nautical charts. For example, researchers saw that reefs, banks and islands were erroneously located or left out entirely in the Chagos Archipelago (left). Landsat provided information to warn sailors in the region until a revised chart (center) included the newly discovered Colvocoresses Reef and adapted position of Speakers Banking company. The Landsat epitome from 2 Apr 2018 (correct) shows the electric current locations of Colvocoresses Reef, Speakers Bank and Blenheim Reef. Image courtesy: Charts from U.S. Defense Mapping Agency, Landsat prototype by Allison Nussbaum.

Landsat'southward synoptic view also proved its worth as a resources for monitoring global crop production. In the early 1970s, the Usa accounted for near 50% of worldwide grain exports and had large stockpiles of wheat. In July 1972, initially unaware of a growing global shortage in wheat harvests, the US sold 15 million tons of wheat at a subsidized depression cost to Soviet traders. Shortly afterwards, the US grain supply plummeted and grain prices soon reached 125-twelvemonth highs in Chicago. Over the side by side year, nutrient prices around the earth rose by fifty%. The Department of Agriculture's Foreign Agricultural Service was instructed to institute a global crop surveillance and reporting system to forestall such major article losses in the future. Landsat data apace became an essential part of this solution and a new emphasis was placed on the use of satellite observations for agricultural objectives and resource monitoring. To effectively forecast crops on a global scale, however, advances in automated processing and quantitative image processing were required.

Evolving from Analogue to Digital

Early on Landsat satellites (ane–3) carried a Return-beam Vidicon (RBV) instrument based on proven television-based technology and a newly developed multispectral scanner system (MSS). The MSS was the outset space-based instrument to digitally encode World information, to obtain calibration information in orbit and to measure data in multiple spectral channels with sufficient geometric allegiance to let meaningful comparisons betwixt those channels. While images tin can exist processed from the MSS's digital data to deport qualitative assay like aeriform photos, the potential to analyse satellite data quantitatively – i.e. quantitative remote sensing – was revolutionary. The MSS quickly proved itself in applications such equally nomenclature of vegetation types and boosted the adoption of digital satellite data for Earth observation, leading to the evolution of more advanced multispectral instruments. This procedure of digital image processing and statistical analysis of data would redefine modern passive remote sensing from space.

Technical characteristics for the side by side generation of multispectral scanner instruments were defined based on applications – specifically agriculture and geologic exploration for the new Thematic Mapper (TM) requirements. The TM instrument would be much more sophisticated, with 30m resolution, seven spectral bands including a thermal infrared band, and continuation of onboard calibration. Optimally, the next mission would include 2 satellites for an 8-day repeat coverage. Landsats 4 and five launched in 1982 and 1984 respectively.

With each new generation of sensors, the needs of the Landsat user community connected to drive requirements for improved spatial and radiometric resolution, spectral and temporal coverage, geolocation and calibration. Landsat 7 launched in 1999 with the Enhanced Thematic Plus (ETM+), which added a panchromatic band for increased spatial resolution and increased thermal ring resolution from 120m to 60m. In 2013, Landsat 8 was launched capturing around 750 scenes a day, an increment from the effectually 450 scenes a day on Landsat 7. The Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) instruments on Landsat 8 accept improved betoken-to-noise ratio and radiometric performance, enabling 12-chip quantization of information and therefore allowing for more bits for better World surface land characterization. While all Landsat satellites take collected calibration data onboard, Landsat 8 added a lunar calibrator to conduct onboard scale using the moon like a photographer'due south 'greyness card'. The evolution of Landsat sensors has consistently improved data quality while maintaining precise scale and backward compatibility within the archive. The data in the US Geological Survey archive from 1972 to the nowadays can be confidently inter-compared, both spatially and radiometrically, confirming Landsat as the cornerstone of global land imaging.

The evolution of sensors onboard each successive Landsat satellite continued to meliorate the apply of Landsat data for multiple applications. Image courtesy: Laura Rocchio and Julia Barsi

Growth of Earth Science Enquiry from Space

Studies and applications of Landsat data continued to aggrandize as this meticulously calibrated annal continued to grow. In June 1988, New England's carbohydrate maple forests were devastated by pear thrip damage. By the time the regime had figured out what was happening, the trees were putting out their second circular of leaves. Admission to archived Landsat data was the merely way scientists were able to accurately map the extent of the defoliation. In the tardily 1980s, scientists set up out to assess global deforestation rates in the tropics using approximately 2,700 Landsat scenes from the archive and a geographic information organization (GIS) to classify pixels into various state cover types and analyse spatial structures. Their results were used to calculate the first apparent and verifiable Amazon deforestation rates – a near-impossible chore with previous labour-intensive and fault-prone field sampling campaigns. These are simply 2 of the many studies that emphasize the importance of a robust worldwide Landsat data archive.

In an effort to privatize and compensate the costs of this national investment, the US regime passed the Land Remote-Sensing Commercialization Act of 1984. This resulted in exponential cost increases for Landsat data, with digital TM scenes costing upwardly to US$iv,400 each. At a time when computing power was increasing and the new field of GIS was budding, orders for Landsat imagery were decreasing – primarily due to the higher costs. These costs put Landsat data largely out of the easily of scientists working on large-scale or long-term studies, prompting some scientists to migrate to other, coarser resolution datasets, like NOAA's Advanced Very High Resolution Radiometer (AVHRR).

Gratis and Open Data Policy Unleashes Full Potential

In 2008, the USGS officially appear no-charge electronic access to any Landsat scene held in the USGS-managed national archive. This was a pivotal decision that removed financial barriers for institutions and researchers and opened up new and previously unimaginable Landsat applications. Prior to the free and open data policy, enquiry was restricted to the data that institutions and researchers could afford, rather than the information that they really needed to solve a problem. Since 2008, there has been a significant increase in the use of Landsat, particularly in global multi-temporal applications such every bit the World Resources Plant Global Forest Watch spider web awarding that monitors global forests in near real time. Geoscience Commonwealth of australia Water Observations from Space uses Landsat data to improve sympathize where h2o is commonly present, for case. The archive is also used by the Global Food Security-Support Analysis Data Croplands database to provide the highest spatial resolution (30m) global cropland map to date. Equally of 31 October 2018, users had downloaded virtually 90 million Landsat scenes from the USGS annal.

Landsat one-8 path/row density map of the over eight million Landsat acquisitions from 25 July 1972 to 31 Oct 2018 that are available for download at the USGS EROS Center's Landsat archive (world wide web.earthexplorer.com). Epitome courtesy: Matt Radcliff

Landsat Global Archive Consolidation Initiative

With the constrained onboard storage capabilities of older Landsat satellites, numerous ground stations around the world paid a fee for the right to receive and distribute Landsat data. These 'international cooperators' (ICs) received Landsat data of their coverage areas downlinked to their local antennas. Each IC applied processing parameters specific to their data usage and placed the data onto distinctive media storage formats. Over time, more Landsat data was held outside the USGS archive, much of it unique. Recognizing the critical value of this information, the USGS began the Landsat Global Archive Consolidation (LGAC) initiative in 2010 to bring the data into a centralized global archive at the EROS Heart. To date, over five million scenes accept been received from IC stations around the globe, with just over 3.5 million of them being unique additions to the Landsat archive. As of mid-2018, the LGAC effort was estimated to be most 80% complete.

Next Generation of Data-commitment and Assay-ready Products

In 2016, the USGS reprocessed the entire global Landsat annal into a tiered 'drove' inventory structure. This structure ensures that all Landsat Level-1 products provide a consistent archive of known data quality to support time-serial analyses and data stacking, while decision-making continuous improvement of the archive and access to all data as it is acquired. The implementation of collections represents a substantial modify in the management of the Landsat archive by ensuring consistent quality through fourth dimension and across all instruments.

With a collection inventory construction in place, the USGS released research-quality, applications-ready, Level-2 science products unremarkably referred to every bit Landsat Assay Ready Information (ARD) in 2017. Landsat ARD consists of tiptop-of-temper reflectance and brightness temperature, surface reflectance and provisional surface temperature. A fundamental goal of ARD is to significantly reduce the preprocessing brunt of Landsat information, assuasive users to easily produce regional and continental-calibration Landsat-based maps of country comprehend, country cover changes and other derived geophysical and biophysical products. In early on 2019, the USGS released a suite of U.s.a. ARD Level-iii science products. These products span the USGS Landsat archive from 1982 to the present and include burned area (representing per-pixel burn classification and burn probability), fractional snow-covered area (indicating the percent of a pixel covered by snow), and dynamic surface water extent (describing the existence and status of surface water). Not only do these Landsat science products significantly reduce preprocessing tasks, they also provide a significant advantage to scientists and land resource managers who monitor changes in the The states's land cover land and condition.

An example of a Landsat 8 analysis-set up data tile h004v002 Level-2 surface reflectance (top left), provisional surface temperature (top eye), Level-3 dynamic surface water extent (top right), burned expanse (lower left) and fractional snow-covered area (lower right) science products acquired on 23 July 2017. Paradigm courtesy: Chris Barnes.

Towards 50 Years of Observations and Beyond

In 2020, NASA will launch Landsat 9, the successor to the notwithstanding-operational Landsat eight satellite, to proceed the mission of unrivalled space-based Earth observation and to lead the Landsat programme into a half-century of Globe imagery provided to users worldwide at no accuse. Together, both satellites will acquire around 1,500 high-quality daily images of the Globe that will accelerate research applications, including our ability to map global surface temperature and continuously track and characterize changes in land cover, use and condition. A joint NASA-USGS Landsat Architecture Study Team was established in 2017 to empathise how the capabilities of future Landsat missions should look beyond Landsat ix. As with previous Landsats, the team will accept into business relationship data user needs as well as new technologies, relevant government policies and commercial and international capabilities.

The success of the Landsat program has inspired the European Infinite Agency (ESA) Copernicus Plan Sentinel-2 satellite constellation, and a new generation of commercial satellite constellations like the RapidEye small-sats, SkyBox small-sats and Pigeon cube-sats. While these small-scale-sat constellations provide college spatial resolution and better temporal coverage than Landsat, they have a reduced spatial coverage per image and reduced spectral capability. At that place volition continue to exist a need for science-grade, rigorously calibrated satellites like Landsat, only there is an untapped potential to leverage the integration betwixt Landsat and these new emerging technologies.

Current monitoring, assessment and projection initiatives provide scientifically accurate land comprehend and land change records. Today, it is necessary to use both big data and data cubes and to harmonize Landsat with other international and commercial datasets in lodge to advance our agreement of the causes – and effects – of natural disasters, urban growth and glacial ice changes for future generations. Landsat's long-term information record provides an unrivalled resource for observing state embrace and land-use change over a timescale of decades. Evolving engineering, free data and robust calibration accept helped make Landsat the cornerstone of global land imaging.