Lesson 1 of 3 · Alos
ALOS: map land with different kinds of measurements
8 minute lesson · 3 checks along the way
Your goal for this lessonDistinguish the ALOS optical and radar branches and interpret a derived land product with appropriate evidence.
In this lesson 3 sections · 3 checks
Using archive links & definitions
Follow a linked name to explore its archive card. “Back to your lesson” brings you to the same part of the reading.
Words with a dotted underline open a short definition right here in the lesson.
Read & understand
Combine sensors for land observation
The Advanced Land Observing Satellite program, ALOS, supports mapping, resource studies and disaster monitoring. The first spacecraft, Daichi, launched in January 2006 with three instruments: PRISM for , AVNIR-2 for visible and near-infrared observations, and PALSAR for L-band radar. These instruments measured different properties, so their data could contribute complementary information about the same landscape.
Stereo views support estimates of surface shape through viewing geometry. Multispectral measurements describe reflected light in selected bands. Radar transmits a signal and records its return. A landscape can therefore look different in each dataset without one image being false: the sensor, wavelength, illumination and processing determine what the displayed values represent.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
Follow the optical and radar branches
ALOS-2, named Daichi-2 in the archive, launched in May 2014 and continued the radar strand with PALSAR-2. ALOS-4 followed in 2024 with PALSAR-3 and a design combining wide coverage with detailed observations. Radar can operate without sunlight and observe through clouds, making it useful when optical views of an affected area are obscured.
ALOS-3 was intended to continue the optical strand but was lost in the failed first H3 launch in March 2023. The numbering does not describe four identical satellites or four successful observation records. Keeping each spacecraft’s instrument and outcome attached to its name prevents an optical image from being misidentified as a radar measurement or an unflown capability from becoming a reported result.
NARITA Masahiro photographed H-IIA Flight 24 launching Daichi-2, also known as ALOS-2, on May 24, 2014. The satellite remains enclosed in the fairing. The image documents launch, not a deployed radar antenna, a land-observation result or the later ALOS-3 mission. Resized and compressed under CC BY-SA 3.0.
Look closely
What evidence would establish the quality of a later ALOS-2 land product?
See what to notice
Instrument calibration, processing documentation, quality information and validation observations are needed. A successful-looking ascent does not establish the accuracy of a derived map.
Check 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
Interpret a land product, not just its colors
ALOS-family datasets include radar mosaics, forest classifications and elevation products. A forest/non-forest map is produced by processing observations with specified methods; it is not a direct photograph of an exact carbon stock. Classification errors, spatial scale and changing acquisition conditions can influence a comparison between years.
For a fictional forest-change study, first check dates, product versions, resolution and classification definitions. Then compare changes with independent observations or field information before attributing them to clearing. A different radar return might reflect moisture or geometry as well as vegetation. Documenting these alternatives makes the map a useful starting point for investigation rather than a self-explanatory verdict.
Check 3 of 3
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Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
Explore further · Optional
Go to the source
Explore the evidence behind this lesson. These optional readings and videos open in a new tab.
- Read: JAXA: original ALOS instruments and purposeHistorical instrument architecture; old future-tense passages do not establish current spacecraft status.
- Read: JAXA: ALOS family and observation productsCompare the explanation and its assumptions with the worked example in this lesson.
- Read: JAXA: ALOS-2 radar capabilitiesCompare the explanation and its assumptions with the worked example in this lesson.
- Read: JAXA: ALOS-4 observation architectureCompare the explanation and its assumptions with the worked example in this lesson.
- Read: JAXA: forest maps and radar mosaicsRead product definitions, versions and validation context; map classes are derived products, not direct photographs of carbon mass.