Bridge falsework and formwork monitoring during construction
High-cadence optical and SAR imagery provides an independent, timestamped record of falsework erection, deck pours and striking, giving project managers and insurers visibility that site diaries alone cannot guarantee.
Sensors
- Planet SkySat: 50 cm native resolution (resampled product delivered at 50 cm), tasked revisit achievable at sub-daily cadence over a fixed site; captures deck pour progress, falsework bay counts and temporary access roads in true colour and NIR
- Airbus Pléiades Neo: 30 cm panchromatic, 1.2 m multispectral, stereo pairs available; enables planimetric change mapping and rough volumetric estimation of falsework towers at system level; revisit 1–2 days over mid-latitudes with tasking
- ICEYE X-band SAR: Spotlight mode delivers approximately 25 cm azimuth resolution; coherence change detection between repeat passes (minimum 1-day repeat with the full constellation) flags introduction and removal of large metallic falsework assemblies as coherence loss events
- Capella Space X-band SAR: Spotlight mode at approximately 35 cm resolution; high backscatter from steel falsework members creates a distinct radar signature against water or soft ground; archive tasking enables retrospective milestone reconstruction
What a satellite can and cannot see on a falsework site
Individual falsework members, typically H-frame or tubular steel props with cross-sections of 100–200 mm, sit well below the resolution floor of any current commercial satellite. No amount of image sharpening changes that. What satellites do resolve is the system: the spatial footprint of a falsework bay cluster, the height signature visible in SAR layover geometry, and the strong X-band radar return produced by large metallic assemblies against a background of water, mud or soft fill.
Monitoring is therefore at the structure level, not the component level. The practical questions a satellite record can answer are: when did falsework first appear in a given span? When was it removed? Does the optical sequence of deck pours match the programme? Are there signs of unplanned reconfiguration between scheduled site visits? These are exactly the questions that matter to a project insurer or a lender's technical adviser who cannot station an engineer on site every day.
SAR coherence as a falsework arrival and departure signal
Interferometric SAR coherence measures how consistently a patch of ground scatters radar energy between two passes. A stable surface, bare concrete or compacted earth, maintains high coherence. Introduce a large steel structure and the scattering geometry changes abruptly: coherence drops. Remove it and, if the underlying surface has not changed, coherence partly recovers. This behaviour is well established in the published literature on urban construction monitoring and is the physical basis for using repeat-pass X-band SAR to track falsework events.
ICEYE and Capella Space both operate in X-band (approximately 9.6 GHz), where metallic targets produce backscatter values that can exceed surrounding terrain by 10–20 dB in spotlight acquisitions. A coherence change map differencing two passes separated by, say, 48 hours will show falsework introduction as a spatially coherent low-coherence patch coinciding with the span under construction. The method does not require ground control points and is independent of cloud cover, which matters on river-valley bridge sites where morning fog is common.
One honest limit: if the river surface beneath the falsework is already incoherent (moving water is always incoherent), the baseline coherence in that zone is already low. Analysts must define the coherence change relative to the adjacent bank or pier areas, not the open water. This is standard practice but worth stating explicitly.
Optical imagery and the deck pour sequence
Concrete deck pours on large bridges follow a strict sequence. Spans are typically cast in segments to control shrinkage and to manage falsework loading, and the construction programme specifies which bays are poured in which order. A 50 cm optical image taken the morning after a pour shows a colour and texture change on the freshly placed concrete relative to the adjacent hardened sections. Pléiades Neo's 30 cm panchromatic band resolves the formwork edge lines well enough to identify which span segment has been cast.
Cloud is the principal constraint. On a site with a 90-day deck pour programme, a run of overcast days can produce gaps of a week or more in the optical record. The practical answer is to run SAR and optical in parallel: SAR provides the all-weather structural change signal, optical provides the interpretable visual confirmation when sky conditions allow. Neither sensor alone is sufficient for a credible independent record.
Building the independent record insurers actually want
Construction all-risk insurers and project finance lenders share a common problem: they rely on contractor-supplied progress reports, which are accurate most of the time and occasionally are not. An independent satellite-derived timeline, archived from first mobilisation to final striking of falsework, provides a check that does not depend on anyone on site remembering to take a photograph.
The deliverable is a timestamped change log: each SAR acquisition pair that shows a coherence event is tagged with a date, a span reference and a classification (introduction or removal). Each optical acquisition that shows a pour is similarly tagged. The combined log can be cross-referenced against the contractor's programme and the insurance policy's milestone schedule. Discrepancies, a pour recorded by satellite three weeks before the insured milestone date, or falsework still present when the programme says it was struck, become visible without requiring an adversarial audit.
Satellize structures this kind of independent monitoring record for infrastructure clients, drawing on tasked commercial constellations alongside open Sentinel-1 C-band data for longer-baseline coherence context. The Sentinel-1 12-day repeat is too slow to catch rapid falsework events reliably, but it provides a useful low-cost archive layer for the quieter phases of a project.
Honest limits of the method
Resolution is the first limit, already noted. The second is geometry. SAR imaging geometry means that tall falsework towers on a narrow bridge deck can produce layover artefacts that obscure the deck surface itself in the radar image. Analysts working on cable-stayed or arch bridges with substantial tower structures need to account for this explicitly in their acquisition planning, selecting look angles that minimise layover over the span of interest.
The third limit is ambiguity in the coherence signal. Heavy rain, changes in soil moisture on the river banks, or the arrival of other large equipment (a crawler crane, a concrete pump) can all produce coherence change events that are not falsework. Interpretation requires an analyst who understands the construction sequence and can distinguish falsework signatures from equipment noise. Automated change detection alone is not sufficient for this application.
Typical figures
| Best optical spatial resolution | 30 cm panchromatic (Pléiades Neo); 50 cm (Planet SkySat) |
| Best SAR spatial resolution | ~25 cm azimuth in spotlight mode (ICEYE); ~35 cm (Capella Space) |
| SAR frequency | X-band (~9.6 GHz) for ICEYE and Capella; C-band (5.4 GHz) for Sentinel-1 as archive layer |
| Tasked revisit cadence | Sub-daily to 1-day for SAR with ICEYE full constellation; 1–2 days optical with Pléiades Neo tasking |
| Minimum detectable falsework footprint | Approximately 5 m × 5 m cluster of steel members at system level; individual props not detectable |
| Cloud penetration | SAR: all-weather. Optical: clear sky required; cloud cover is the primary gap risk |
| Coherence change detection latency | 24–48 hours after second acquisition in a pair, depending on processing pipeline |
| Archive depth | Sentinel-1: from 2014. Commercial tasking archives: from constellation launch dates (ICEYE from 2018, Capella from 2020, SkySat from 2013) |
| Typical delivery formats | GeoTIFF change maps, KML/KMZ overlays, timestamped event log (CSV or PDF), GIS-compatible vector layers |
Analytics Satellize can run
| Falsework introduction and removal event log | SAR coherence change detection (interferometric pair differencing, X-band spotlight) | Timestamped CSV log with span reference, event type and coherence magnitude; delivered within 48 hours of each acquisition pair |
| Deck pour sequence map | Optical change detection on multispectral imagery; texture and colour classification of fresh versus cured concrete | Annotated GeoTIFF and PDF report showing poured segment extents with acquisition date |
| Programme conformance check | Cross-referencing satellite event log against contractor-supplied Gantt chart milestones | Milestone comparison table flagging confirmed, early, late or unverified events; issued at agreed reporting intervals |
| SAR backscatter anomaly alert | Threshold-based backscatter change detection in X-band spotlight acquisitions | Automated alert (email or API push) when a significant backscatter change is detected outside a scheduled event window |
| Falsework footprint planimetric map | Manual digitisation and semi-automated object detection on 30–50 cm optical imagery | Vector polygon layer (GeoJSON or Shapefile) showing falsework cluster extents per acquisition date |
| Independent construction record archive | Systematic tasking and archiving of SAR and optical acquisitions from project mobilisation to practical completion | Structured image archive with metadata, change logs and narrative summary report suitable for insurer or lender review |
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.