Earth Observation Satellites: From Landsat to High-Resolution Commercial Imaging

Landsat as the Backbone of Civil Earth Observation

Among all Earth observation initiatives, the Landsat program stands out for longevity and continuity. Its roots go back to the launch of the Earth Resources Technology Satellite in July 1972, a mission that was later renamed Landsat in 1975. Over the decades, Landsat has become the reference point for long-term environmental monitoring because of its consistent, publicly valuable imagery record.

A major late-20th-century milestone was Landsat 7, launched in April 1999. The satellite carries eight spectral bands, with spatial resolutions spanning roughly 15 to 60 meters and a 16-day revisit cycle, supporting repeatable observation of land surface change over time.

Landsat Program History: Sensors, Policy, and a Near Collapse

The MultiSpectral Scanner (MSS), one of the foundational Landsat sensors, was designed in 1969 and deployed as early as the autumn of 1970. The program’s institutional home and funding approach later shifted dramatically. In 1979, President Carter transferred Landsat operations from NASA to NOAA and pushed for a long-term operational framework, including additional satellites beyond Landsat 3 and a transition toward private-sector involvement.

That privatization materialized in 1985, when the Earth Observation Satellite Company (EOSAT) operated Landsat under a ten-year contract. EOSAT ran Landsats 4 and 5, held exclusive rights to market Landsat data, and was also positioned to build Landsats 6 and 7. The arrangement, however, proved vulnerable to government budget uncertainty.

By 1989, NOAA’s Landsat funding was drying up. With insufficient appropriations, NOAA directed Landsat 4 and 5 to be shut down. Emergency funding—organized via Vice President Quayle in his role heading the newly formed National Space Council—kept the program alive, but the next two years remained unstable. In 1990 and 1991, Congress provided only about half of the annual funding NOAA needed, and agencies that benefited from Landsat data were expected to cover the shortfall through data sales.

In October 1992, the Land Remote Sensing Policy Act (Public Law 102-555) authorized procurement of Landsat 7 and aimed to ensure continued availability of digital Landsat imagery at low cost. In practice, the political and budget backing required to fully stabilize operations did not arrive quickly enough. By the end of 1992, EOSAT stopped processing Landsat data entirely.

The program then suffered a major technical setback. Landsat 6 launched on October 5, 1993, but was lost during launch. The failure could have ended the continuity of civil imaging capabilities, delaying progress in Earth observation for science and public use. Instead, EOSAT resumed processing Landsat 4 and 5 data in 1994, and NASA eventually launched Landsat 7 in April 1999. In hindsight, much of the drama might have been avoided if the 1992 policy mandate had been fully supported and funded when enacted.

SPOT: France Builds High-Resolution Optical Observation

While Landsat was establishing a long record of moderate-resolution monitoring, France began developing SPOT (Système Pour l’Observation de la Terre) in the late 1970s. Initiated by CNES, the program was designed to strengthen understanding and management of Earth systems by supporting resource analysis, forecasting and detecting phenomena linked to climatology and oceanography, and monitoring human activity alongside natural processes.

SPOT combined satellites with a ground infrastructure for programming, control, image production, and distribution. Launches were conducted using ESA Ariane rockets—Ariane 2, 3, and 4—while SPOT Image, headquartered in Toulouse, marketed the imagery globally. By May 2002, SPOT 5 extended capability into 2.5, 5, and 10 meter products, enabling higher detail applications compared with Landsat’s typical scales.

The SPOT orbit was engineered as polar, circular, and sun-synchronous. From an altitude of about 832 km and an inclination of roughly 98.7°, the system was designed so the ground track geometry and Earth’s rotation would allow coverage of any terrestrial point approximately every 26 days, with more frequent revisit possible through off-nadir pointing.

SPOT 1, 2, and 3: Early Operational Success and End-of-Life

SPOT satellites began operational imaging in 1986 and produced more than 10 million high-quality images over time. SPOT 1 launched in February 1986 on Ariane 2 and, within days, returned imagery at 10–20 meter resolution. SPOT 2 entered orbit in January 1990, and SPOT 3 followed in September 1993.

These early satellites carried two High Resolution Visible (HRV) instruments that could operate together or independently, using panchromatic and multispectral modes. Panchromatic imagery delivered 10 meter resolution, while three multispectral bands—green, red, and near-infrared—were captured at 20 meters. Scene coverage was approximately 3,600 km², with revisit intervals ranging from about 1 to 4 days depending on latitude and pointing strategy.

Panchromatic sensing typically spans the visible and near-infrared range, often displayed in grayscale though false-color presentations are possible. Multispectral systems measure several discrete bands simultaneously—often three to seven—while hyperspectral systems, increasingly pursued later, may collect dozens to hundreds of bands.

Operational life eventually ended for the early SPOT platforms. After SPOT 1’s orbit was lowered in 2003, it gradually lost altitude and disintegrated in the atmosphere. SPOT 2 underwent a controlled deorbit beginning mid-July 2009, culminating with a final burn and reentry burn-up on 29 July 2009. SPOT 3 ceased operations due to stabilization problems.

SPOT 4 and SPOT 5: Expanded Spectral Reach and Stereo Capability

SPOT 4, launched in March 1998, retained key geometric traits of earlier satellites, including a 60 km swath per instrument and oblique viewing capability of about 27° on either side of nadir. Its major enhancement was the addition of a Short Wave Infrared (SWIR) band, broadening analytical potential for vegetation, moisture, and material discrimination.

SPOT 5 launched in May 2002 to maintain service continuity with improved image quality. It carried two High Resolution Geometrical (HRG) instruments, delivering 2.5–5 meter panchromatic products and 10 meter multispectral imagery, with SWIR at 20 meters in the 1.58–1.75 μm range. SPOT 5 also included a panchromatic stereo imaging capability, pointing forward and backward to acquire near-simultaneous stereo pairs and support terrain relief mapping.

SPOT 6 and SPOT 7: Constellation Planning and High-Throughput Imaging

SPOT 6 and SPOT 7 were planned for launches in 2012 and 2013 to form a constellation intended to provide continuity of high-resolution, wide-swath imagery up to about 2023. The specification emphasized 1.5 meter panchromatic output, 8 meter multispectral, and 1.5 meter color-merged products, supporting disaster management and mitigation use cases.

The design included simultaneous panchromatic and multispectral capture across bands such as Panchromatic (450–745 nm), Blue (450–525 nm), Green (530–590 nm), Red (625–695 nm), and NIR (760–890 nm), with a footprint around 60 km by 60 km and daily acquisition capacity up to roughly 3 million km². The Indian Space Research Organization launched SPOT-6 on a Polar Satellite Launch Vehicle on September 8, 2012, alongside a 15-kg Japanese microsatellite.

GeoEye: OrbView, Ikonos, and Sub-Meter Commercial Imaging

GeoEye developed into a major commercial Earth imaging provider operating a constellation capable of collecting millions of square kilometers of map-accurate imagery monthly and archiving it for long-term access. The company’s earlier identity traces to Orbital Imaging Corporation (ORBIMAGE), founded in 1992 as a division of Orbital Sciences Corporation, enabled by the 1992 Land Remote Sensing Policy Act that opened the door for private companies to enter high-resolution imaging.

A notable early mission was OrbView-2, launched in 1997. By modern standards it is low resolution, but it captured broad-area color imagery with about 1 km ground resolution, supporting science research, agricultural and ocean monitoring. OrbView-2 proved highly successful and remained in use for years. GeoEye later rebranded in 2006 after acquiring Space Imaging for $58 million, bringing IKONOS and OrbView assets under one umbrella.

GeoEye imagery fed major web mapping ecosystems, supplying vast coverage to Microsoft and Yahoo, and providing Google with exclusive online mapping access from GeoEye-1. The firm also became a significant supplier to the National Geospatial-Intelligence Agency, competing primarily with DigitalGlobe and SPOT Image while pushing commercial imaging below the 1 meter threshold.

IKONOS: The First Widely Available 1 Meter Commercial Satellite Imagery

IKONOS was the first commercial Earth observation satellite to provide publicly available imagery at both 1 meter (panchromatic) and 4 meter (multispectral) resolution, with commercial availability beginning January 1, 2000. Its name derives from the Greek eikōn, meaning “image.” The satellite originated as Lockheed Martin’s Commercial Remote Sensing System (CRSS). In April 1994, Lockheed Martin received one of the first commercial licenses for high-resolution imagery, and in October 1995, Space Imaging was licensed to transmit satellite telemetry in the 8 GHz Earth Exploration Satellite Services band.

Two spacecraft were envisioned. The initial 1999 launch of IKONOS-1 failed when the Athena rocket payload fairing did not separate, preventing orbit insertion. The successor spacecraft—originally planned as IKONOS-2—was renamed IKONOS and launched in September 1999 from Vandenberg Air Force Base. It flies a polar, circular, sun-synchronous orbit at about 681 km altitude, with both sensors covering an 11 km swath.

Technically, IKONOS used a 0.7 m primary mirror and a folded 10 m optical focal length in a five-mirror design, with a honeycomb mirror structure to reduce mass. The focal plane detectors included a panchromatic sensor with 13,500 pixels and a multispectral sensor with 3,375 pixels. Instrument mass was about 171 kg and power draw roughly 350 watts. Spectral acquisition supported a 1 m panchromatic band spanning approximately 0.45–0.90 μm and multispectral bands in blue (0.445–0.516 μm), green (0.506–0.595 μm), red (0.632–0.698 μm), and near-infrared (0.757–0.853 μm), with 4 m multispectral and 1 m pan-sharpened products. Revisit performance was roughly 3–5 days off-nadir and about 144 days at true nadir, with a 98-minute orbital period around 680 km altitude.

OrbView Series and GeoEye-1 / GeoEye-2

OrbView-2, also known as SeaStar, collected true-color daily imagery of land and oceans and was widely used to infer oceanographic conditions for fishing maps. It offered broad 2,800 km swaths and supported naval operations, environmental monitoring, and crop assessments, using its SeaWiFS optical and near-infrared multiband sensor for scientific research, particularly for studying ocean–atmosphere gas exchange and phytoplankton production. Data collection ceased in December 2010.

OrbView-3, launched in 2003, acquired 1 m panchromatic and 4 m multispectral imagery in 8 km swaths, collecting up to about 210,000 km² per day with revisits under three days. In April 2007, GeoEye reported OrbView-3 no longer produced usable imagery, and its orbit decayed to a controlled reentry into the Pacific in March 2011.

GeoEye-1, previously known as OrbView-5, launched September 6, 2008 and separated successfully from its Delta II vehicle 59 minutes after liftoff. It delivered 41 cm panchromatic and 1.65 m multispectral imagery across 15.2 km swaths from a sun-synchronous orbit at about 684 km altitude with roughly 98° inclination and imaging capability up to 60° off nadir.

GeoEye-2 was scheduled for launch in 2013 with a planned 25 cm resolution, with Lockheed Martin selected to build the satellite platform. The intent was to deliver imagery quality comparable to the best Cold War era aerial photography.

DigitalGlobe: QuickBird, Google Earth, and the WorldView Era

DigitalGlobe’s corporate lineage began in 1993 as WorldView Imaging Corporation, then EarthWatch Incorporated in 1995, and finally DigitalGlobe in 2002. In 1993, the U.S. Department of Commerce granted the company the first license for a private enterprise to build and operate a high-resolution satellite imaging system for commercial sale.

In October 2001, DigitalGlobe launched QuickBird from Vandenberg Air Force Base, achieving the world’s highest-resolution commercial satellite at the time. Two prior attempts from Russia were unsuccessful, but QuickBird entered service and remained operational for years. The QuickBird success established DigitalGlobe as a key supplier to both government and commercial markets, including a pivotal agreement to provide high-resolution imagery to Keyhole Corporation—acquired by Google in 2004—which became central to Google Earth and accelerated the mainstream rise of online mapping portals.

In September 2003, DigitalGlobe won a major $500 million contract with the National Imagery and Mapping Agency (NIMA) under the NextView program, supporting a new generation of commercial satellites. The company proceeded with WorldView-1 and WorldView-2 development, acquired GlobeXplorer in January 2007 to strengthen online imagery access and services, and launched WorldView-1 in September 2007 on a Boeing Delta II. Full operational capability began in November 2007, making DigitalGlobe the first firm to deliver NextView imagery.

By early 2009, DigitalGlobe expanded distribution through agreements with Google, Microsoft (Virtual Earth), and partners including Oracle, NAVTEQ, and Nokia, integrating imagery into Nokia Location Services through streamlined delivery formats. WorldView-2 launched successfully on October 8, 2009 from Vandenberg, bringing DigitalGlobe’s sub-meter satellite count to three and enabling a high collection capacity on the order of 500 million km² annually. WorldView-2 also distinguished itself as the only commercial high-resolution satellite offering 8-band multispectral capability, paired with advanced agility and accuracy.

Remote Sensing Momentum and Continuity

From Landsat’s decades-long civil record to SPOT’s optical high-resolution advances and the commercial push to sub-meter imaging by GeoEye and DigitalGlobe, Earth observation has evolved through a mix of policy decisions, funding disruptions, sensor innovation, and market expansion. The recurring theme across these programs is continuity: sustained imagery availability depends not only on hardware but on stable operational commitments, robust distribution infrastructure, and the ongoing ability to refresh capabilities as technology and user demand progress.