A clean coastal mosaic and a 25-year time-lapse in Earth Engine
Two Google Earth Engine tools for the coast near Bunyu Island: a seamless Sentinel-2 mosaic, and a multi-sensor Landsat time-lapse from 1998 to today.
- Year
- Ongoing
- Role
- Personal project
- Tools
- Google Earth Engine (JavaScript), Sentinel-2, Landsat Collection 2
Why build these
A field report describes a coast at one moment. Imagery that is clean and consistent through time lets anyone, technical or not, see how that coast changes.
A seamless Sentinel-2 mosaic
Large, high-resolution exports of the coast kept failing or looking patchy. Working through it meant solving:
- Memory limits on large exports in Earth Engine.
- Visible seams where image tiles meet.
- Uneven colour stretch between scenes.
Tile edges are blended with a focal-mean feather, and everything is projected in UTM zone 50N (EPSG:32650) so it lines up with local field data.
Landsat time-lapse, 1998 — today
One frame per period, from several Landsat sensors, made to look like one continuous record:
- Collection 2 Level-2 surface reflectance with the correct scaling.
- Cross-sensor harmonisation (Roy et al., 2016) so older and newer sensors line up.
- Cloud masking from the QA_PIXEL band.
- Gaps filled from nearby dates only, so each frame stays true to its own time.
What I learned
Most of the work in a good time-lapse is invisible: consistent scaling, honest gap-filling and careful masking. Getting those right is what makes the change on screen real rather than an artefact.