Satellite stereo imagery vs. lidar for open pit volume surveys
How stereo photogrammetry and airborne lidar each build a DEM for pit volume work, and why the choice comes down to mobilization versus tasking.
Both methods get you to the same place: an elevation surface you can difference against last month's surface to get a moved-material number. How they build that surface, and what it costs to get one every month, is where they split.
How each one builds the surface
Lidar sends laser pulses down from an aircraft and times the return. Enough pulses over enough ground gives you a dense point cloud, which gets classified and gridded into a digital elevation model. It's an active sensor: it makes its own light, so it works at night and sees through gaps in thin vegetation.
Stereo photogrammetry works differently. You take two overlapping images of the same ground, shot from slightly different positions (two passes of a satellite, or two frames from an aircraft), and triangulate elevation from the parallax between them, the same principle behind depth perception in binocular vision. No laser, no active sensor. Just geometry worked out from two pictures.
For an open pit, both approaches end up at a DEM. The difference is in what it takes to get the sensor over your site.
Where each one actually fits a pit
Lidar's advantage has always been canopy penetration: send enough pulses through gaps in a forest and some reach bare ground, which is why lidar dominates forestry and corridor mapping. An open pit doesn't have that problem. Benches, haul roads, the pit floor, the stockpiles, it's bare rock and graded surfaces with nothing for a laser to punch through that a camera can't already see directly.
That's the case for stereo imagery on a working pit: the terrain that makes lidar worth its mobilization cost in a forest isn't present here. A stereo pair off very-high-resolution satellite or aerial imagery resolves the same bare-ground elevation without needing an aircraft tasked to fly a lidar sensor over your specific coordinates.
DEM accuracy: what actually matters for a volume check
Vendors publish absolute accuracy numbers for both lidar and stereo DEMs, worth asking for when you're validating a single surface against survey control. For a month-over-month volume read, consistency between the two dates matters more than either number on its own: same sensor type, same processing pipeline, same resolution, so the difference between July's surface and August's surface reflects material moved. Mixing a lidar DEM from one quarter with a stereo-derived DEM from the next introduces exactly the kind of offset that gets mistaken for extraction volume, or masks volume that was really there.
Cost: mobilization versus tasking
This is the practical dividing line for anyone running this check every month rather than once. Airborne lidar means mobilizing an aircraft and flight crew to the pit, scheduling around weather and airspace, then repeating that mobilization for the next read. That cost structure makes sense for a one-time baseline survey or an annual flyover. It gets expensive fast as a monthly cadence, and it depends on someone scheduling and paying for a flight every time.
Satellite stereo tasking doesn't require a crew near the site at all. An order goes in, the satellite passes over on its normal orbit or a tasked revisit, and the imagery comes back for processing into a DEM. There's no aircraft to charter and no weather window to coordinate beyond cloud cover over the pit on the day of the pass.
A financier or planner needs an independent monthly number set against the mine plan or a covenant, read after read. That tasking model scales to a monthly cadence without a mobilization line item every time. A monthly extraction read built this way, elevation surface over elevation surface, no site visit required, is the whole premise behind Pit Progression.
If a monthly volume number against plan is what you're after, that's the one thing the product is built to deliver.