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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Henrik Forstén’s drone carries a homebuilt synthetic aperture radar (SAR) payload that collects measurements along programmed flight paths. Processing those measurements combines them into detailed radar imagery; the 2026 update also demonstrates repeat-pass interferometric SAR, which uses phase differences to estimate elevation. Forstén reports that the radar and drone hardware together cost about 1,000 EUR—not an exact under-$900 price—and says the custom hardware is not for sale.
How the drone turns a flight into a radar image
A conventional radar measurement gives information about targets in its field of view. SAR builds on measurements collected as the radar moves: it records distance and phase at successive positions, and processing uses those observations to synthesize a larger aperture. The result can show finer angular detail than a single measurement. The scene must remain static during the synthetic-aperture measurement.
In the original build, the radar supports four polarization combinations: HH, HV, VH, and VV. Polarization describes the orientation of the transmitted and received radar waves; it gives the system multiple ways to measure how the scene reflects radar energy. The output is radar imagery, not an ordinary camera photograph.
How autonomous capture is planned and controlled
Mission planning and status
Forstén’s custom ground-control program plans linear, circular, and interferometric SAR missions. It lets the operator configure radar settings—including sweep length, pulse repetition frequency, and polarization—and view radar and drone status. The flight controller runs ArduPilot and relays position and timing information to the radar, linking each radar measurement to the aircraft’s movement.
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Transit and capture speeds
For the settings described in the 2026 account, the drone can travel faster between measurement areas than while collecting data. Forstén limits transit to 10 m/s for safety and uses a 5 m/s capture speed to collect more measurements over a given distance and improve image quality. These are the author’s reported settings for this project, not universal flight recommendations.
The original 2025 account describes an example flight at 110 m altitude, along an approximately 500 m straight track, at about 5 m/s. Those figures describe that example, not a required mission profile.
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What the imagery shows—and what it does not prove
Forstén’s 2026 account presents an approximately 1,000 m × 1,000 m full-scene view and a 400 m × 500 m detail view alongside satellite imagery. In the radar image, field paths are visible, and light poles appear as bright returns even though they are barely visible in the satellite comparison. The examples illustrate what the system captured; they do not establish a quantitative resolution figure.
The imagery workflow estimates trajectory deviations with GPGA, then uses fast factorized backprojection, antenna-pattern weighting, and a digital elevation model (DEM) to form the image. A Lee speckle filter is applied afterward. Forstén reports 17,000 radar sweeps and an output grid of 4,156 × 16,473 pixels for the described processing workload.
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On an RTX 3090 Ti, Forstén reports 22 seconds for autofocus and 0.9 seconds for image formation per polarization. Those are author-reported times for this workload and GPU, not general performance guarantees. The account also names lidar from Finland’s National Land Survey as a comparison reference.
How the repeat-pass elevation example works
The 2026 update demonstrates interferometric SAR by comparing measurements from repeat passes. Forstén flew the same track and direction twice, with a 1 m elevation difference between the passes. Processing the phase difference between the measurements can estimate elevation.
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Forstén’s stated rationale for flying in the same direction is to help cancel common timing errors and avoid a velocity-related Doppler phase difference that can arise when comparing opposite-direction passes. This describes the geometry and reasoning in his example, not a universal prescription for interferometric missions.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What “under $900” means—and what the build cost
The “under $900” wording comes from Hackster.io’s secondary headline. Forstén’s September 14, 2026 primary account instead reports about 1,000 EUR for the radar and drone hardware together. The figures use different currencies and come from different sources; the headline should not be treated as an exact price for the current build.
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In his February 11, 2025 original account, Forstén described spending approximately 200 EUR on the drone and 600 EUR on two radar PCBs, and said the project took about 10 months of his personal time. These are project-account figures, not independently audited costs. The later hardware total and the earlier component figures refer to different accounts of the build and should not be combined into a single budget.
This is a custom project, not a ready-to-buy radar drone. Forstén says the hardware is not for sale. The original account describes a low-cost, no-name 7-inch FPV kit as the basis for the drone; that is a general platform description, not an exact model identification or proof that a current kit can reproduce the demonstrated system. A DIY platform would also need to accommodate the radar payload and support compatible flight control, navigation, and mission operation.
What is available to other builders
Forstén says the SAR processing code is available in the torchbp GitHub repository under the MIT license. That makes the processing code accessible, but does not make the custom radar hardware a product or establish that the complete system can be reproduced from the repository alone.
Sources: Henrik Forstén, “Interferometric Synthetic Aperture Radar Drone” (September 14, 2026); Henrik Forstén, “Homemade polarimetric synthetic aperture radar drone” (February 11, 2025); Hackster.io, “Henrik Forstén’s Radar Drone Captures Detailed Imagery on Autonomous Flights — for Under $900”.
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