Bonded warehouse rooftop expansion as trade volume proxy
Bonded warehouse and free-trade-zone rooftop growth, tracked through optical time-series, gives a spatially explicit, lagging signal of import and re-export demand at specific customs nodes. Combining building-footprint change detection with cadastral overlays separates trade-policy-sensitive storage from general logistics expansion.
Sensors
- Sentinel-2 MSI: 10 m resolution in visible and near-infrared bands, 5-day revisit at the equator with both satellites. Sufficient to detect new rooftop footprints above roughly 1,000 sq m and to track construction phase transitions across quarters. Free archive from 2015.
- Planet Basemaps (PlanetScope): 3 m resolution, near-daily revisit. Resolves individual warehouse bays and can distinguish rooftop material (bare concrete, metal cladding, membrane) useful for construction-stage classification. Commercial licence required.
- Airbus SPOT 6/7: 1.5 m panchromatic, 6 m multispectral. Useful for confirming footprint boundaries and reading rooftop features such as loading-bay count. Revisit 1 to 3 days with off-nadir tasking. Tasked on demand.
- Google Earth Engine archive: Provides access to historical Landsat and Sentinel-2 stacks for retrospective baseline construction. Landsat archive extends to 1972 at 30 m; useful for decade-scale context on zone establishment, not individual building detection.
Why rooftop area is a credible, if slow, trade signal
Bonded warehouses are not built on speculation in the way that general logistics sheds sometimes are. They require a customs authority licence, a defined catchment of importers or re-exporters, and often a sovereign guarantee or free-trade-zone concession. That regulatory overhead means construction correlates tightly with anticipated throughput: operators do not sink capital into bonded space unless demand is already contracted or the policy environment has changed materially.
The catch is timing. From planning approval to operational status, a large bonded facility typically takes twelve to thirty months. Rooftop area therefore lags the trade signal by several quarters. That makes it a poor tool for spotting this month's import surge but a useful one for reading medium-term structural shifts, such as a customs zone positioning itself for a new preferential trade agreement or a port authority responding to a sustained increase in transshipment volumes.
Separating bonded from general logistics: the cadastral overlay problem
Optical imagery alone cannot tell a bonded warehouse from an ordinary distribution centre. The rooftops look identical. The separation requires a second data layer: cadastral or zoning records that delineate customs-controlled parcels, free-trade-zone boundaries, or special economic zone perimeters. In jurisdictions where these boundaries are published (many are, as they carry legal force for duty exemption), a simple spatial join assigns each detected building footprint to a regulatory category.
Where cadastral data is unavailable or out of date, a reasonable proxy is proximity to a designated port or inland customs depot, combined with building morphology. Bonded facilities tend to be larger than average, set back from public roads, and clustered inside a perimeter fence that itself appears in imagery. Neither heuristic is watertight. A customs-zone boundary that has not been publicly gazetted will defeat the method entirely, and that is worth stating plainly before any client commits to this signal.
The practical workflow: ingest the zone boundary as a polygon, clip the building-footprint change-detection output to that polygon, and report gross roofed area by quarter. Changes outside the polygon are filtered out. Changes inside it are attributed to bonded capacity growth.
Building-footprint change detection: what the methods actually do
The core technique is bi-temporal or multi-temporal image differencing on a normalised spectral index. New rooftops appear as high-reflectance anomalies in the shortwave infrared relative to the pre-construction baseline, which is typically bare soil or low vegetation. Sentinel-2 Band 11 (1.6 µm SWIR) is particularly responsive to the transition from soil to sealed surface. A threshold applied to the change image, followed by morphological filtering to remove small artefacts, yields candidate new-building polygons.
Cloud is the principal operational constraint. Tropical free-trade zones, which are some of the most active globally, can see ten or more consecutive cloud-contaminated Sentinel-2 acquisitions during monsoon season. The standard mitigation is to use the full available time-series and composite the clearest observations per quarter rather than relying on any single date. Planet's near-daily cadence helps here: the probability of at least one cloud-free acquisition per week is substantially higher at 3 m daily than at 10 m every five days, though Planet data carries a licence cost that Sentinel-2 does not.
Minimum detectable footprint at 10 m Sentinel-2 resolution is roughly 400 to 1,000 sq m depending on rooftop contrast and surrounding land cover. A standard bonded warehouse bay is typically 5,000 sq m or larger, so the resolution is adequate for the target class. Smaller ancillary structures, guard posts, generator housings, are below the detection floor and should not be counted.
Reading the lag: construction phase to operational throughput
A quarterly rooftop-area time-series can be segmented into three observable phases. First, site clearance and slab preparation: spectral reflectance rises, vegetation indices drop, but no enclosed roofed area yet exists. Second, structural framing: roofed area begins to appear as bays are enclosed, often non-uniformly across a large shed. Third, operational fit-out: the roof is complete but the facility may not be accepting cargo for several more months while racking, fire suppression, and customs fitments are installed.
Translating rooftop completion into a throughput forecast requires an assumption about the lag between phase three and first cargo movement. Published data on free-trade-zone development timelines is thin, but infrastructure analysts typically apply a six-to-twelve-month lag for large bonded facilities. Clients should treat any throughput estimate derived from rooftop data as a range, not a point forecast, and should cross-reference against port statistics or trade declarations where those are published.
Honest limits of the signal
Rooftop expansion is a one-directional indicator in most optical time-series: buildings appear but rarely disappear. A bonded facility that is decommissioned or converted to general warehousing will not vanish from the footprint count unless the roof is physically demolished. This creates a survivorship bias in long-run area totals. Analysts should check for vacancy signals, such as absence of truck activity or faded rooftop markings in high-resolution imagery, before treating stable rooftop area as stable throughput.
The method also cannot distinguish utilisation rate from capacity. A zone may double its bonded rooftop area while actual throughput stagnates if the new space is built ahead of demand. Rooftop area is a capacity proxy, not a flow proxy. For flow, the correct sibling signal is vehicle or container activity at the facility, covered in separate pages in this library.
Satellize runs this type of footprint time-series as part of its broader analytics stack. The Tonga crop-estimation programme uses a similar change-detection pipeline on agricultural parcels; the bonded-warehouse application substitutes industrial land-cover classes and a customs-zone polygon as the spatial filter.
Typical figures
| Spatial resolution (primary sensor) | 10 m (Sentinel-2 MSI, visible and SWIR bands) |
| Spatial resolution (validation) | 1.5 m panchromatic (SPOT 6/7 on-demand tasking) |
| Revisit cadence | 5 days at equator (Sentinel-2 A+B combined); near-daily (Planet PlanetScope) |
| Minimum detectable rooftop footprint | 400 to 1,000 sq m at 10 m resolution, depending on rooftop-to-background contrast |
| Archive depth | Sentinel-2 from 2015; Landsat for decade-scale context from 1972 at 30 m |
| Key spectral bands | Sentinel-2 Band 4 (red, 665 nm), Band 8 (NIR, 842 nm), Band 11 (SWIR, 1610 nm) for surface-change detection |
| Cloud sensitivity | High in tropical zones; quarterly compositing required; Planet daily cadence reduces gap risk |
| Cadastral overlay requirement | Published customs-zone or free-trade-zone boundary polygon needed to separate bonded from general logistics |
| Throughput lag estimate | 6 to 30 months from construction start to operational status (range from infrastructure literature) |
| Delivery formats | GeoTIFF change layers, GeoJSON footprint polygons, quarterly area time-series in CSV or GIS layer |
Analytics Satellize can run
| Quarterly bonded rooftop area index | Bi-temporal SWIR change detection on Sentinel-2 time-series, clipped to customs-zone polygon | GIS layer and CSV time-series showing gross roofed area by quarter per designated zone |
| Construction phase classification | Multi-date spectral segmentation distinguishing slab, framing, and enclosed-roof stages using Planet 3 m imagery | Per-building status report updated monthly, with phase label and estimated completion quarter |
| New footprint alert | Threshold-based change detection on rolling 90-day Sentinel-2 composite, filtered by minimum area and zone boundary | Alert feed (GeoJSON or email) triggered when a new enclosed footprint above 2,000 sq m appears within a monitored zone |
| Retrospective capacity growth curve | Annual Sentinel-2 and Landsat archive stack processed through supervised land-cover classifier to extract impervious industrial area | Decade-scale rooftop area time-series per zone, delivered as chart-ready CSV and annotated PDF |
| Multi-zone comparative ranking | Standardised area-growth rate calculated across a portfolio of user-specified customs zones, normalised by zone perimeter area | Quarterly ranking table of zones by capacity growth rate, with map overlay in GIS format |
| Vacancy indicator flag | Cross-reference of stable rooftop footprint against vehicle-activity proxy (truck presence in high-resolution imagery) to flag potentially underutilised facilities | Flagged facility list with supporting imagery thumbnails, updated quarterly |
Who does the work
We can get this done for you. Satellize runs its own analyst desk and a strong science team. You do not buy a data feed and work out what it means; our people source the imagery, run the analysis described on this page, and hand you the answer with its confidence limits stated. Discuss this requirement.