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Ground Truth AsiaAsian remote sensing, read from the ground

An independent magazine on satellite remote sensing across Asia

The Asian landscape, read from orbit and checked on the ground

An independent magazine on satellite remote sensing across Asia: where the data comes from, what it shows of the continent, and how field checks make the maps honest.

Start with the dataHow floods are mapped
Aerial view at dawn of a wide tropical river delta, brown silt water branching between bright green rice paddies, thin morning mist over the tree lines, deep blue sky lightening to orange on the horizon, documentary aerial photography, natural colors.
Dawn over a river delta: brown silt water branching between bright green paddies, the working landscape of half the continent's remote sensing.

Three desks

One continent, three questions

Where the images come from, what they show of Asian land, water and cities, and how the people who use them keep the maps honest. Each desk opens onto its own index of guides.

  1. A researcher at a wooden desk studying a large printed satellite map of a river delta under a magnifying loupe, notebook and pencils nearby, warm desk lamp in a dim archive room, shallow depth of field.
    Desk 01

    Satellites and Data

    Where the images come from: the open archives, the national fleets of Japan, India, Korea, Thailand and China, and the weather satellites that never blink.

    3 guides inside

  2. A wide tropical river in monsoon spate carrying brown water between green banks, a wooden ferry crossing, heavy grey sky about to release rain, dark reflections on the water.
    Desk 02

    Land, Water and Cities

    What the images show of the continent: monsoon floods, rice harvests, megacities on the move and haze that ignores borders.

    4 guides inside

  3. Researchers of several nationalities talking in small groups beside poster boards in a conference hall between sessions, lanyards and coffee cups in hand, warm interior light.
    Desk 03

    Methods and Community

    How the work is done and argued over: ground truth, free software, classification and the annual conference circuit.

    4 guides inside

Recent dispatches

Latest from the desks

New guides as they are filed: free imagery, real-time weather, flood mapping, urban growth, field validation and the conference archive.

  • A student on a library ladder browsing long shelves of archive boxes and film canisters in a university map library, cool daylight falling from high windows, quiet atmosphere.

    Satellites and Data

    Free Satellite Imagery of Asia

    Landsat and Sentinel-2 cover all of Asia every few days at no cost. What each archive offers, how to search by place and date, and what the scenes cannot do.

    Landsat and Sentinel-2 cover all of Asia at no cost.

  • A large typhoon spiral seen from high above the ocean, dense white cloud bands curling around a small dark eye, deep blue sea visible at the edges of the storm, sunlight from the left.

    Satellites and Data

    Himawari: Asian Weather from Orbit in Real Time

    From the equator the Himawari satellites photograph Asia and the Pacific every ten minutes. How forecasters, sailors and flood teams read that stream.

    The whole disk photographed every ten minutes.

  • A flooded village seen from a small wooden boat at dusk, half-submerged houses and palm trees, brown flood water reflecting an orange sky, silhouettes of people watching from a rooftop.

    Land, Water and Cities

    Mapping Asian Floods From Orbit

    When monsoon rivers rise, radar satellites see through cloud and map the water. How flood extent maps are built and used, from relief to river basin planning.

    Radar finds the water under monsoon cloud.

  • Aerial view of a dense Asian megacity at dusk, apartment towers packed to the horizon fading into warm haze, construction cranes at the outskirts, city lights beginning to glow.

    Land, Water and Cities

    How Asian Megacities Grow, Seen From Orbit

    Jakarta, Dhaka, Manila and Chengdu keep spilling outward. How image time series measure urban growth, and why planners watch the fringe, not the skyline.

    The fringe grows faster than the skyline.

  • A field surveyor in rubber boots standing in a green paddy field, recording notes in a waterproof notebook beside a marked wooden survey stake, handheld GPS receiver, clear morning light.

    Methods and Community

    Ground Truth: Validating Satellite Maps in the Field

    Every land-cover map rests on points someone walked to. How field campaigns are planned, what a GPS record proves, and why honesty about errors matters.

    Map points someone walked to.

  • Long shelves of bound conference proceedings volumes in a university library, spines in faded colors, one open volume resting on a reading table under a warm lamp.

    Methods and Community

    The ACRS Proceedings, Year by Year

    Four decades of Asian Conference on Remote Sensing papers, from mimeographed 1980 sessions to PDF sessions: what the proceedings hold and where to find them.

    Four decades of papers, free to read.

Desk 1 of 3

Satellites and Data

Where the images come from: the open archives, the national fleets of Japan, India, Korea, Thailand and China, and the weather satellites that never blink.

  • A student on a library ladder browsing long shelves of archive boxes and film canisters in a university map library, cool daylight falling from high windows, quiet atmosphere.

    Satellites and Data

    Free Satellite Imagery of Asia

    Landsat and Sentinel-2 cover all of Asia every few days at no cost. What each archive offers, how to search by place and date, and what the scenes cannot do.

    Landsat and Sentinel-2 cover all of Asia at no cost.

  • A clean-room technician in white coveralls and blue gloves inspecting a gold foil wrapped satellite body under bright laboratory lamps, reflections on the polished floor.

    Satellites and Data

    Asia's Own Earth Observation Satellites

    Japan's ALOS, India's Cartosat, Korea's KOMPSAT, Thailand's THEOS and China's Gaofen fleet: what each national mission observes and who can order its images.

    ALOS, Cartosat, KOMPSAT, THEOS, Gaofen.

  • A large typhoon spiral seen from high above the ocean, dense white cloud bands curling around a small dark eye, deep blue sea visible at the edges of the storm, sunlight from the left.

    Satellites and Data

    Himawari: Asian Weather from Orbit in Real Time

    From the equator the Himawari satellites photograph Asia and the Pacific every ten minutes. How forecasters, sailors and flood teams read that stream.

    The whole disk photographed every ten minutes.

Open the satellites and data index

Desk 2 of 3

Land, Water and Cities

What the images show of the continent: monsoon floods, rice harvests, megacities on the move and haze that ignores borders.

  • A flooded village seen from a small wooden boat at dusk, half-submerged houses and palm trees, brown flood water reflecting an orange sky, silhouettes of people watching from a rooftop.

    Land, Water and Cities

    Mapping Asian Floods From Orbit

    When monsoon rivers rise, radar satellites see through cloud and map the water. How flood extent maps are built and used, from relief to river basin planning.

    Radar finds the water under monsoon cloud.

  • Farmers transplanting bright green rice seedlings by hand into a flooded paddy, reflections in the still water, terraced fields rising behind them under soft overcast light.

    Land, Water and Cities

    Rice Paddies Seen From Orbit

    Rice grows in flooded fields that satellites read well. How time series track planting, flooding and harvest, and why forecasts start with a good paddy map.

    A paddy season followed week by week.

  • Aerial view of a dense Asian megacity at dusk, apartment towers packed to the horizon fading into warm haze, construction cranes at the outskirts, city lights beginning to glow.

    Land, Water and Cities

    How Asian Megacities Grow, Seen From Orbit

    Jakarta, Dhaka, Manila and Chengdu keep spilling outward. How image time series measure urban growth, and why planners watch the fringe, not the skyline.

    The fringe grows faster than the skyline.

  • A busy elevated city road disappearing into thick grey haze at midday, the sun a pale disc through the smog, distant towers barely visible, muted colors.

    Land, Water and Cities

    Watching Asian Air Pollution From Orbit

    Haze does not stop at borders. Sensors such as Sentinel-5P and GOSAT track the gases above Asian cities, and the maps feed health advisories.

    The haze season has a satellite clock.

Open the land, water and cities index

Desk 3 of 3

Methods and Community

How the work is done and argued over: ground truth, free software, classification and the annual conference circuit.

  • Long shelves of bound conference proceedings volumes in a university library, spines in faded colors, one open volume resting on a reading table under a warm lamp.

    Methods and Community

    The ACRS Proceedings, Year by Year

    Four decades of Asian Conference on Remote Sensing papers, from mimeographed 1980 sessions to PDF sessions: what the proceedings hold and where to find them.

    Four decades of papers, free to read.

  • A field surveyor in rubber boots standing in a green paddy field, recording notes in a waterproof notebook beside a marked wooden survey stake, handheld GPS receiver, clear morning light.

    Methods and Community

    Ground Truth: Validating Satellite Maps in the Field

    Every land-cover map rests on points someone walked to. How field campaigns are planned, what a GPS record proves, and why honesty about errors matters.

    Map points someone walked to.

  • Two staff members at desktop computers showing colorful map layers in a small district office, paper maps pinned on the wall, a ceiling fan, rainy season light through the window.

    Methods and Community

    Google Earth Engine and QGIS: Free Analysis Tools

    One tool computes on petabytes in the cloud, the other runs offline on a district laptop. How QGIS and Earth Engine share one analysis workflow.

    Petabytes in the cloud, finished maps on a laptop.

  • A speaker gesturing beside a large projected satellite image of a river delta in a dark lecture hall, rows of attentive listeners fading into the background.

    Methods and Community

    ACRS: Asia's Annual Remote Sensing Conference

    Since 1980 the Asian Conference on Remote Sensing has moved from capital to capital, publishing open proceedings. What happens there and how to take part.

    The annual meeting, capital to capital since 1980.

Open the methods and community index

Where to start

Three doors for a first visit

A rice season followed from orbit, the two free tools that carry an analysis, and the satellite clock of the haze season: three guides that explain what the desk does better than any definition.

  • Farmers transplanting bright green rice seedlings by hand into a flooded paddy, reflections in the still water, terraced fields rising behind them under soft overcast light.

    Land, Water and Cities

    Rice Paddies Seen From Orbit

    Rice grows in flooded fields that satellites read well. How time series track planting, flooding and harvest, and why forecasts start with a good paddy map.

    One image is a photograph; a season of them is a map.

  • Two staff members at desktop computers showing colorful map layers in a small district office, paper maps pinned on the wall, a ceiling fan, rainy season light through the window.

    Methods and Community

    Google Earth Engine and QGIS: Free Analysis Tools

    One tool computes on petabytes in the cloud, the other runs offline on a district laptop. How QGIS and Earth Engine share one analysis workflow.

    Two free tools carry a whole analysis workflow.

  • A busy elevated city road disappearing into thick grey haze at midday, the sun a pale disc through the smog, distant towers barely visible, muted colors.

    Land, Water and Cities

    Watching Asian Air Pollution From Orbit

    Haze does not stop at borders. Sensors such as Sentinel-5P and GOSAT track the gases above Asian cities, and the maps feed health advisories.

    A satellite clock for the haze season.