Mumbai High-Speed Rail — UAV & Bathymetric Survey

Project Overview

BTPL carried out a combined UAV and bathymetric survey along a 30 km stretch of the Mumbai High-Speed Rail (Bullet Train) alignment for Afcons. The work brought the land and water portions of the corridor under a single geodetic framework, so that developed ground, creeks and water bodies could be represented as one continuous surface. Deliverables were prepared in CAD and GIS formats suited to alignment design and construction planning.

Client Requirement

The survey was required to provide a current and dimensionally consistent record of the corridor for alignment design, structure and foundation planning, and quantity assessment. Land topography alone is not sufficient where an alignment crosses creeks and tidal water, so bed levels had to be captured in the same datum as the ground survey. The same dataset also serves as a base for utility, encroachment and land interface studies along the route.

Project Challenge

• An urban and peri-urban corridor with dense built-up development, constrained access and multiple property and land-use interfaces
• A combined land and water scope, requiring a continuous transition between photogrammetric ground data and sounded bed levels at the creek and waterbody crossings
• Tidal influence in the creek reaches, which governs the workable window for sounding and requires all soundings to be reduced to a common water level reference
• Shallow and obstructed margins where boat access is limited, calling for supplementary RTK observation to close the survey to the bank line
• UAV operations in an urban environment, where airspace clearance, third-party safety and existing rail and road infrastructure restrict flying windows

BTPL Approach

BTPL began by establishing a primary and secondary control network along the corridor using GNSS observations tied to published reference stations, with control extended by DGPS/RTK so that the land and water components share a common datum. UAV missions were planned corridor-wise with adequate forward and side overlap, with flight blocks sized to airspace and access constraints and pre-marked ground control and independent check points distributed across each block. The water sections were surveyed by echo sounder with positioning from the same GNSS framework, running sounding lines with cross lines and check lines across the channel and referencing soundings to observed water levels. Shallow margins beyond safe boat draught were picked up by RTK observation so that the sounded surface closes to the surveyed bank line. The land and water datasets were then merged into a single continuous surface through the crossings.

Data Processing

Aerial imagery was processed through aerial triangulation using the surveyed ground control to generate a dense point cloud, from which the DSM, bare-earth DTM and orthomosaic were derived after classification and editing. Bathymetric soundings were reduced for transducer draft, sound velocity and observed water level, then filtered and gridded before being merged with the terrestrial surface. Contours, cross sections and longitudinal sections were extracted from the combined surface and prepared in CAD and GIS formats.

Quality Control

Check points were observed independently of the control used in the photogrammetric adjustment, and the derived surface was verified against those withheld check points and against RTK-observed ground spot levels. Bathymetric quality was assessed through cross-line and check-line comparison at line intersections, together with bar checks and sound velocity observation during acquisition. Deliverables were reviewed internally for datum consistency, surface continuity across the land and water join, and completeness against the agreed scope before release.

Result

Afcons received a single terrain and bathymetric model covering the 30 km stretch of the corridor, with land and water sections referenced to a common datum and without the need to reconcile separate surveys. The dataset supports alignment refinement, structure and foundation planning, quantity estimation and construction planning along the route.