Key takeaways
- Bidders price the uncertainty they cannot see. A dated, measurable capture of the site narrows the guess and narrows the contingency that comes back in the price.
- The point is not a prettier tender document. It is that every bidder reads the same ground, so the bids you compare differ on method and margin rather than on what each of them assumed.
- Issue the capture as a priced bid document with a stated capture date, method and accuracy, not as an unlabelled image dropped in an appendix.
- Licence wording decides whether a bidder may use the data at all. State that bidders may use it for pricing the work, and state what happens to the licence for the party who wins.
- The capture that settles a claim later is the one taken before anyone moved dirt, so the pre-tender flight doubles as the pre-construction baseline.
- Say plainly what the capture does not warrant: it is a surface record of visible conditions on one date, and it is not a subsurface or geotechnical investigation.
- Fly it early enough that the processed deliverables are in the package when it is issued, not as an addendum after questions start arriving.
Most aerial capture on a construction or earthworks project happens after someone has been awarded the work. The contractor arrives, flies the site, and finds that the ground does not match the assumption in their bid. What follows is a change order, or an argument, or both.
The cheaper sequence is to fly the site before it goes out for bid, and to hand the result to every bidder as part of the tender package. The flight costs the same either way. The difference is who is carrying the uncertainty when the prices come in.
Why the owner's flight beats the winner's flight
A bidder who cannot see the ground prices the risk of what might be there. That contingency is real money, it is invisible in the submitted number, and you pay it whether or not the risk materialises. Several bidders pricing the same unknown will price it differently, which is why two bids on the same scope can be far apart for reasons that have nothing to do with how either firm would do the work.
Put a dated, measurable record of the site in front of all of them and three things change at once. The contingency shrinks because the unknown shrinks. The bids become comparable, because the differences left are method, productivity and margin rather than each firm's private guess about the stockpile in the northeast corner. And the awarded contractor starts work from the same picture the owner had, which removes the most common opening move in a site-condition dispute.
There is a fourth benefit that only shows up later. A capture taken before anyone mobilised is the only true before image you will ever have of that site, and it is worth having for reasons that have nothing to do with the tender.
What to capture
A pre-tender flight is a scoping exercise, not a full engineering survey, and the deliverable list should reflect that. In most cases it is:
- An orthomosaic of the whole site at a resolution good enough to read surface conditions, access, drainage and what is stored where. This is the item bidders will actually look at. How to read one without being a surveyor is covered in how to read an orthomosaic.
- A terrain surface and contours so bidders can estimate earthworks quantities rather than assume them. The distinction between a surface that includes everything standing on the site and one filtered to bare ground matters here, and is set out in DSM vs DTM.
- Volumes for anything already stockpiled on site, with the base surface and method stated. Material already there is material the winning contractor either uses or moves, and both have a price.
- Oblique imagery of access routes, laydown areas, adjacent properties and any structure that will constrain the work.
- A short method note giving the capture date, weather and ground conditions, the control used and the accuracy achieved.
What makes this package work is the method note, not the imagery. An unlabelled picture in an appendix invites bidders to discount it. A capture with a date, a stated accuracy and a named method is a document they can rely on, and a document you can point at afterwards.
The licence wording, which is the part most packages miss
Aerial data is licensed, not simply handed over. If you commissioned the capture, the terms between you and the drone contractor decide what you may do with it, including whether you may distribute it to third parties. Issuing it to a bid list is distribution. The scope of what you own and what you may pass on is the subject of data ownership and retention on drone jobs, and it needs settling before the package is assembled rather than after a bidder asks.
Two sentences in the tender documents cover the rest:
- Grant a bounded licence to bidders. Say that the aerial data is provided for the sole purpose of preparing a bid on this project, that it may not be reused or redistributed, and that unsuccessful bidders are to destroy or return their copies.
- Say what the successful bidder gets. The winner usually needs a broader licence, because they will load the surface into their own software and work from it. Saying so up front avoids negotiating a licence after award, when leverage has already moved.
Alongside the licence, state the disclaimer plainly. The capture represents visible surface conditions on the stated date, to the stated accuracy, and is not a geotechnical or subsurface investigation. Bidders remain responsible for their own site examination. That sentence does more to prevent an argument than any amount of additional imagery, and it is honest: a drone sees the surface, and the honest limits of aerial capture apply here exactly as they do anywhere else.
What it does to site-condition claims
A differing site-conditions claim usually turns on one question: what did the ground look like when the contract was priced, and who is in a position to prove it. When neither party has a dated record, the argument is reconstructed from photographs taken at various times by various people for other reasons, and it is resolved by negotiation rather than evidence.
A pre-tender capture changes that question into a documentary one. There is a surface, a date and a method, it was issued to the claimant as part of the documents they priced from, and the comparison against today is arithmetic rather than opinion. What makes a capture hold up in that setting is the same thing that makes any aerial record defensible: a stated date, an unedited original retained, and a method that can be described. The habit of comparing a built surface against the design surface is covered in as-built versus design surface.
It is worth being clear about scale. This does not make claims impossible, and it is not a substitute for a geotechnical program. It removes the subset of disputes that exist only because nobody wrote down what the site looked like.
Timing, and the addendum trap
The flight has to be early enough that processed deliverables are in the package when it is issued. A capture that arrives as an addendum three days before close is worse than no capture, because bidders have already priced the unknown and will not reprice on short notice, and because an addendum invites a question period extension.
Work backwards from the issue date. Allow for the flight itself, for processing and delivery, and for the weather window: Alberta sites lose days to wind, and the time from flight to deliverable is the subject of how long from flight to deliverable. Booking two to three weeks ahead of the tender issue date is comfortable for most sites. Booking the week before is a gamble on wind.
Season matters too. A site captured under snow gives bidders a less useful picture of surface conditions than the same site in September, and a winter surface carries its own caveats, covered in surveying stockpiles and sites under snow. If the tender date is fixed and the only available window is a snow-covered one, say so in the method note and let bidders weight it accordingly.
Who else uses the same capture
The tender is the reason you commissioned it, but the same dataset usually earns its keep three or four more times on the same project:
- As the pre-construction baseline for progress comparison, which is the basis of the monitoring cadence discussed in how often should you re-fly a site.
- As the reference the owner's own team uses in design reviews and constructability discussions.
- As the dated record a lender, insurer or board asks for when the project is reported on.
- As the starting quantity for any earthworks reconciliation during the job.
That is the real economics of a pre-tender flight. The cost sits in the owner's budget once and is recovered across the tender, the baseline and the reporting, instead of being priced into every bid as a contingency and then paid again by the winner after award.
Scoping it with a contractor
Tell the drone contractor what the capture is for. A tender capture has different priorities from a monthly progress flight: whole-site coverage matters more than tight accuracy on one corner, obliques of access and adjacency matter more than usual, and the method note is a deliverable rather than paperwork. The accuracy specification, deliverable list and other cost drivers are set out in the cost drivers on an Alberta drone survey quote, and the clauses worth writing into the request are in what to put in a drone survey RFP.
If you are issuing a project to tender in the next couple of months, the question to settle now is whether the ground is going out with the drawings or whether each bidder will be guessing at it separately. Only one of those is free.