Lesson 1 of 4 · Choose a land observation
Choose a land observation
6 minute lesson · 3 checks along the way
Your goal for this lessonMatch a land-mapping question to optical, stereo or active radar measurements.
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.
Read & understand
Start with the question
The Advanced Land Observing Satellite program, ALOS, connects land mapping with environmental observation and disaster information. Original ALOS launched in January 2006. Its PRISM instrument used stereo views for elevation mapping; AVNIR-2 observed land in visible and near-infrared wavelengths; PALSAR supplied active L-band radar observations. These were complementary measurements, not three interchangeable cameras.
Imagine an original mapping assignment with two requests: identify a changing pattern of fields and estimate the height of a ridge. A useful plan states what each measurement contributes before choosing an attractive image. A color pattern and an elevation estimate answer different questions, even when they cover the same landscape.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
Supply illumination when sunlight is unavailable
Daichi-2, also called ALOS-2, continued the radar branch. Its PALSAR-2 transmits microwaves and measures returning signals, enabling observations at night and through cloud. The signal is radar backscatter: energy returned toward the instrument. It is not the visible color that a person would see from an aircraft.
In an original decision exercise, a cloud-covered region needs nighttime observations. An active radar instrument offers a relevant capability. That choice does not by itself determine which roads are open or which buildings are damaged. Those are interpretations requiring suitable data and corroboration, rather than properties guaranteed by the instrument’s name.
H-IIA Flight 24 lifts off from Tanegashima carrying Daichi-2, also known as ALOS-2, on May 24, 2014. Photograph by NARITA Masahiro, CC BY-SA 3.0. Satellite enclosed in the fairing; full source frame retained, display copies resized and compressed only.
Look closely
What can this launch view establish about the later land-observation products?
See what to notice
It records the launch event with the spacecraft enclosed. Product quality requires the later instrument observations, calibration and processing evidence.
Check 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
Keep the branches and outcomes distinct
ALOS-3 was an optical successor, but it was lost in the failed H3 launch on March 7, 2023. ALOS-4, carrying PALSAR-3 radar, launched on July 1, 2024. Numbered successors therefore do not form a simple sequence of successful, identical missions. JERS-1 belongs in the earlier observing heritage rather than being renamed as an ALOS spacecraft.
The launch photograph shows H-IIA Flight 24 carrying ALOS-2 in 2014. It documents transport to space; the satellite is still inside the fairing. To evaluate an actual land map, move beyond the launch record to the instrument, observation time, processing method and validation evidence.
Check 3 of 3
10 pointsUse the reading above. You can try again without losing points.
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.