ALOS-2

ALOS-2, designated by NORAD catalog number 39766 and internationally identified as 2014-029A, is a Japanese Earth observation satellite operated by the Japan Aerospace Exploration Agency (JAXA). Launched on May 24, 2014 (May 23 at 20:00 Eastern Daylight Time), it represents the second generation of Japan's Advanced Land Observing Satellite program, following the original ALOS spacecraft that concluded its operations prior to this successor's development. Weighing 2,120 kg at launch and constructed by Mitsubishi Electric, ALOS-2 — also known by its informal Japanese name Daichi-2, meaning "land" — carries a synthetic aperture radar system designed to support a broad range of Earth observation applications. As of the time of writing, the satellite remains in orbit and operational.

Mission and Purpose

The Advanced Land Observing Satellite program was established by JAXA to provide consistent, high-quality radar-based imaging of Earth's land surface for a variety of civil and scientific applications. ALOS-2 continues and expands on this mandate, with its primary instrument — the Phased Array type L-band Synthetic Aperture Radar 2, or PALSAR-2 — serving as the centerpiece of the satellite's capabilities.

Where the original ALOS carried a suite of instruments that included two optical imaging cameras alongside its L-band radar, ALOS-2 was deliberately redesigned to drop the optical payload. This decision was not a step backward in capability but a pragmatic engineering and budgetary choice: by focusing resources entirely on the radar system, JAXA and Mitsubishi Electric were able to deliver a significantly more capable and refined PALSAR-2 instrument without the complexity and cost burden of maintaining multiple, fundamentally different sensor types on the same platform.

The PALSAR-2 radar is a notable advancement over its predecessor. It retains a survey mode offering approximately 10-meter resolution — a capability inherited from the original PALSAR instrument — but adds higher-resolution spotlight imaging modes that allow the satellite to focus on specific areas of interest with considerably finer detail. Synthetic aperture radar operates independently of sunlight and can penetrate cloud cover, making ALOS-2 useful for monitoring terrain and surface change in regions where optical imagery is frequently obscured by weather. This makes the satellite particularly valuable for disaster response, where cloud cover often coincides with the storms, floods, or volcanic events that require rapid assessment.

Beyond terrain observation, ALOS-2 carries two supplementary instruments that extend its utility. The SPAISE2 system is an automatic identification system receiver designed to detect and track ships at sea, enabling the satellite to contribute to maritime domain awareness by collecting positional data transmitted by ocean-going vessels. The second supplementary payload, the Compact Infrared Camera (CIRC), detects thermal infrared signatures. In addition to its utility for wildfire detection and environmental monitoring, CIRC has been discussed in the context of providing early warning data relating to heat sources on the ground and at sea, broadening the satellite's relevance beyond conventional land observation.

Taken together, ALOS-2's instrument suite positions it as a multi-purpose asset: primarily a land surface observer capable of high-resolution radar mapping, but also a contributor to maritime monitoring and infrared sensing missions. The satellite catalog entry does not publicly specify a detailed mission type or current operational status, and those specifics are not reflected here.

Orbit and Tracking

ALOS-2 operates in a sun-synchronous orbit (SSO), a near-polar orbital regime commonly used by Earth observation satellites. In a sun-synchronous orbit, the satellite's orbital plane precesses at a rate that keeps it roughly aligned with the direction of the Sun throughout the year, meaning the satellite passes over any given location at approximately the same local solar time on each revisit. This consistency is operationally valuable for a radar satellite like ALOS-2 because it allows systematic, repeatable passes that simplify the scheduling of data acquisitions and support change-detection analysis over time.

The orbital parameters tracked for ALOS-2 reflect a nearly circular orbit. The apogee — the satellite's farthest point from Earth's surface — stands at 636 km, while the perigee — its closest approach — is 634 km, a difference of only 2 km. This extremely low eccentricity confirms the orbit is very nearly circular, which is standard for remote sensing satellites that require uniform imaging geometry. The orbit is inclined at 97.9° relative to the equatorial plane, consistent with the retrograde, slightly-past-polar inclination characteristic of sun-synchronous orbits at this altitude. At these orbital parameters, ALOS-2 completes one full revolution of the Earth approximately every 97.3 minutes, meaning it orbits the planet roughly 14 to 15 times per day.

The combination of polar inclination and consistent altitude gives ALOS-2 global coverage capability, including the polar regions, over repeated observation cycles. This allows systematic mapping of the Earth's surface, with revisit intervals determined by the satellite's ground track repeat pattern.

ALOS-2 is cataloged in the NORAD tracking system under ID 39766, and its international designator 2014-029A identifies it as the primary payload of the 29th launch of 2014. It continues to be tracked as an active object in low Earth orbit.

Design and Operator

ALOS-2 was built by Mitsubishi Electric Corporation, one of Japan's primary aerospace manufacturers, under contract to JAXA. The satellite has a launch mass of 2,120 kg, placing it in the medium-to-large category for Earth observation spacecraft. Its design reflects a focused approach: rather than carrying a broad instrument complement, the satellite is optimized around the PALSAR-2 radar, with the supplementary SPAISE2 and CIRC payloads adding value without driving the fundamental architecture.

JAXA, the Japan Aerospace Exploration Agency, is the satellite's operator. JAXA was established in 2003 through the merger of three predecessor Japanese space institutions and has since managed a range of civilian space programs spanning launch vehicles, planetary science, and Earth observation. The ALOS series represents one of JAXA's sustained commitments to domestic Earth observation capability, providing Japan with independent access to radar imagery of the land surface for both scientific and disaster-management purposes.

The choice of L-band radar for PALSAR-2, rather than higher-frequency C-band or X-band systems used by some other Earth observation satellites, has specific technical implications. L-band radar, with its longer wavelength, penetrates vegetation canopy more effectively than shorter-wavelength alternatives, making it better suited to mapping forested areas, monitoring deformation in vegetated terrain, and measuring soil moisture. This capability is particularly relevant for a country like Japan, which has significant forested area and a geography prone to seismic activity, landslides, and severe weather.

Significance and Current Status

ALOS-2 occupies an important role in the international constellation of synthetic aperture radar satellites. Its L-band capability is relatively uncommon in the current Earth observation landscape — most operational SAR satellites operate at C-band or X-band — which means ALOS-2 provides data that is not readily replicated by other systems. This has made it a resource not only for Japanese domestic applications but also for the international scientific and disaster response communities.

Since its launch in May 2014, ALOS-2 has been involved in observational campaigns following major earthquakes, volcanic eruptions, and flood events around the world. Its ability to acquire imagery through cloud cover and darkness makes it a recurring asset when rapid surface deformation or inundation mapping is needed. JAXA has participated in international disaster charter activations and collaborative Earth observation efforts through which ALOS-2 data has been made available to emergency responders in affected countries.

The satellite's longevity — remaining in orbit more than a decade after launch — reflects robust engineering, though the publicly available catalog data does not specify the current operational or health status of the spacecraft. Planning for successors to the ALOS lineage has been underway, but ALOS-2 itself continues to be tracked as an orbiting payload as of the information available here.

How to Spot ALOS-2

ALOS-2 orbits at an altitude of approximately 635 km in a sun-synchronous, near-polar orbit, which means it passes over most locations on Earth at some point during the course of each day. However, as a medium-sized spacecraft without large reflective solar panels comparable to those of crewed stations or some communications satellites, it is not among the most visually prominent objects in low Earth orbit.

Under favorable conditions — when the satellite passes during the twilight period after sunset or before sunrise, while the ground observer is in darkness and the satellite is still illuminated by sunlight — ALOS-2 may be briefly visible to the naked eye as a steadily moving point of light crossing the sky. The best viewing opportunities occur during these twilight windows, particularly in the days following or preceding the satellite's local solar time crossings. Using the orbital parameters listed on this page and a current propagation tool, observers can calculate upcoming passes for their specific location and determine whether any given overpass will occur at a favorable geometry for naked-eye observation.