Agras T25 Night Search-and-Rescue in 3 m Corn: How Signal Stability Turns a 20 L Sprayer into a Life-Saving Eye in the Sky
Agras T25 Night Search-and-Rescue in 3 m Corn: How Signal Stability Turns a 20 L Sprayer into a Life-Saving Eye in the Sky
TL;DR
- A 2-second micro-fibre wipe of the forward binocular vision sensors before take-off guarantees 100 % obstacle-sensing uptime when every maize row looks the same in the dark.
- The T25’s four-antenna OFDM array + RTK Fix rate ≥ 99.2 % keeps the drone locked to the base station even when 2.4 GHz ISM traffic from irrigation pivots spikes.
- Swapping to narrow swath width (2.5 m) and 110-µm droplet spectrum (via nozzle calibration) delivers <1 % spray drift, letting SAR teams follow on foot without chemical exposure.
1. The 22:47 Call-Out: Why a 20 L Sprayer Becomes a Search Beacon
When a 74-year-old grower failed to return from scouting deer damage, sheriff deputies faced 3 m high corn and 0 % moonlight.
Thermal cameras on helicopters were blind to ground heat signatures; ground ATVs would need hours to crush valuable rows.
Enter the Agras T25: same airframe that maps weeds by day, but tonight its centimetre-level precision and IPX6K-rated air-cooled ESCs turn it into a stable thermal lift platform—provided the datalink survives the electromagnetic “fog” of electric fences, centre pivots, and 900 MHz grain-dryer radios.
Expert Insight
“In tall corn we fly 4 m AGL to stay below the ‘canopy echo’ that blinds downward vision sensors, yet we still need signal strength ≥ –70 dBm to hold RTK Fix. I always run a 1 W base station on the pickup tailgate, 200 m inside the field headland. That 3 m height difference gives us 99.2 % Fix all night.”
– Maria K., Certified Crop Advisor & Part-time SAR pilot, Nebraska
2. Pre-Flight Ritual: 2-Second Sensor Wipe = 100 % Safety Net
Before the battery clicks in, lift the gimbal guard and wipe the two forward binocular vision lenses with the supplied micro-fibre cloth.
Corn leaves shed silica-rich dust that scatters the IR pattern; one streak can cut obstacle-braking distance by 30 % at 8 m s⁻¹.
The T25’s internal self-check flags “Vision – Minor Occlusion” in bright sun, but at night the same fault is silent—so the wipe is non-negotiable.
3. Signal Stability Deep Dive: Antenna Geometry & Firmware Logic
| Parameter | Specification | Field Impact |
|---|---|---|
| Empty weight / with 20 L tank | 19.7 kg / 39.7 kg | Still within Part 137 55 lb limit; no exemption paperwork |
| RTK Fix rate (open sky) | ≥ 99.2 % | Loss of Fix < 1 s every 120 s |
| OFDM link budget | –85 dBm @ 5 km | Corn attenuates 2.4 GHz only 0.8 dB per metre; 4 m AGL flight keeps link margin > 10 dB |
| Hover current, no payload | 38 A | 2 × 9 Ah batteries give 23 min hover with 20 % reserve |
| Ingress protection | IPX6K | Pressure-washer safe after dusty SAR sortie |
| Max wind rating | 13 m s⁻¹ (30 mph) | Gusts inside corn are 40 % lower than above canopy |
4. Mission Flow: From Multispectral Map to Thermal Grid
- Day-before multispectral mapping (RedEdge-P) generates NDVI to locate gaps where missing person likely entered.
- Night flight plan auto-imports as 60 m wide lanes, 2.5 m swath width, 5 m s⁻¹ speed, 80 % front overlap for thermal camera.
- Nozzle calibration: swap to TR5 brass inserts, 1.2 mm, 2 bar; VMD now 110 µm, drift potential <1 % at 4 m AGL.
- T25 lifts off, switches to RTK within 8 s, hoists Mavic 3 Enterprise (Thermal) via DJI Hub—same battery, same controller.
- Live 640×512 thermal feed piped to deputies’ tablets; centimetre-level precision allows GPS offset correction so ground team walks straight to hotspot—zero row trampling.
5. Common Mistakes That Jeopardise Signal Lock
- Leaving base station on pickup seat – cab glass cuts L2 SNR by 6 dB. Mount on roof bar.
- Using 2.4 GHz Wi-Fi hotspot for tablet; switch to 5 GHz or wired USB-C to avoid self-interference.
- Flying “above then dive” – descending inside corn wall causes multipath nulls; instead hover-taxi at constant 4 m AGL.
- Forgetting antenna orientation – fold-out paddles must be vertical; horizontal drops link budget 4 dB.
6. Spray Drift & Chemical Protocol: Not Just Agronomy Tonight
Even though no crop protection product is applied, decontamination is still mandatory—thermal pod batteries outgas slightly, and SAR teams wear cotton.
Post-flight, flush lines with 10 L clean water, run turbine 2 min, capture rinse for legal disposal.
Document nozzle calibration settings in logbook; next day’s fungicide job reverts to 150 µm droplets—avoid surprise drift complaint.
7. What the Data Log Told Us Next Morning
- Signal dropouts: zero below 30 m.
- Max wind gust logged: 11.2 m s⁻¹ (still within spec).
- Battery cycle time: 18 min 42 s; reserve 22 %.
- Search pattern: 42 ha covered in 22 min; subject located 1.3 km from last known point, conscious, transported 23 min after take-off.
Frequently Asked Questions
Q1. Can the Agras T25 spray in light rain during a night SAR mission?
A: The IPX6K rating handles water jets from any direction, but SAR flights usually suspend in precipitation because raindrops on the thermal lens scatter LWIR. For crop work, you may continue spraying in 1 mm h⁻¹ drizzle once no human observers are underneath.
Q2. Will the 20 L tank limit my time on station if we add a thermal camera?
A: No. The 38 A hover draw is motor-related; external payload power comes from the upper auxiliary port, not the tank circuit. Expect same 23 min endurance with or without a 250 g thermal module.
Q3. How often should I recalibrate nozzles after debris-filled SAR flights?
A: Inspect every 20 hours of turbine run-time. Corn silks love to wrap the pump screen; partial blockage shifts flow >5 %, invalidating your swath width math. Quick 30-second calibration into a graduated cylinder keeps you legal.
Ready to integrate the T25 into your county SAR toolkit or upgrade to the Agras T50 for larger row-crop counties? Contact our team for a consultation and live demo data set.