Equipment Specifications & Inspection Methodology
Complete technical documentation for our thermal inspection platform: camera specifications, ground sample distance at operating altitudes, calibration procedures, and how the specifications relate to solar PV thermographic inspection topics addressed by IEC TS 62446-3.
This page is intended for solar O&M engineers, asset managers, and procurement teams evaluating inspection providers. All specifications are from manufacturer datasheets unless otherwise noted. We distinguish between manufacturer specs, calculated values, and our operational parameters.
Primary Equipment
Thermal Camera: Autel EVO II Dual 640T RTK V3
| Parameter | Specification | Source |
|---|---|---|
| Sensor Type | Uncooled VOx microbolometer | Manufacturer |
| Resolution | 640×512 radiometric | Manufacturer |
| Pixel Pitch | 12 µm | Manufacturer |
| Focal Length | 13mm | Manufacturer |
| Spectral Range | 8-14 µm (LWIR) | Manufacturer |
| NETD | ≤50 mK @ 30°C (typical) | Manufacturer |
| Temperature Accuracy | ±3°C or ±3% of reading (whichever greater) | Manufacturer |
| Accuracy Environment | −20°C to +60°C environment | Manufacturer |
| Accurate Measurement Distance | 2–20 m accurate measurement distance | Manufacturer |
| Radiometric Output | R-JPEG with full per-pixel temperature matrix (14-bit) | Manufacturer |
| Frame Rate | 30 Hz | Manufacturer |
What NETD Means in Practice
The sensor's published NETD describes thermal sensitivity under specified conditions; it does not establish individual-cell or incipient-defect detection in delivered field data.
Important Caveats
- Accuracy valid only within stated environmental range; performance outside range is unspecified
- Quantitative temperature readings require 2–20 m standoff; beyond 20 m treat values as qualitative unless validated
- Thermal sensitivity (NETD) degrades at elevated ambient temperatures
RGB Visual Camera
Resolution: 50 MP (4K video)
Sensor: 1" CMOS with mechanical shutter
Output: DNG (RAW) + JPEG with EXIF GPS metadata
The RGB camera provides visual documentation of physical damage, soiling patterns, vegetation encroachment, and installation issues. Thermal and RGB images are captured simultaneously with aligned fields of view for defect correlation.
RTK GPS Positioning
| Parameter | Specification |
|---|---|
| Manufacturer Camera Position (Horizontal, RTK Fix) | 1 cm + 1 ppm |
| Manufacturer Camera Position (Vertical, RTK Fix) | 1.5 cm + 1 ppm |
| RTK Network | RTK corrections via NTRIP when network and cellular conditions support a fix |
| Fallback Mode | ±1–1.5 m GPS fallback if RTK signal lost |
Aircraft Operating Limits
Operating Temperature
−10°C to +40°C
Wind Resistance (Manufacturer)
27 mph (12 m/s) maximum
Operational Limit (Thermal Inspections)
14 mph (6 m/s) — our operational ceiling for thermal inspections
Flight Time
~38 min (varies with payload and conditions)
Aircraft operating temperature range is DIFFERENT from thermal camera accuracy range Wind resistance affects radiometric measurement accuracy (wind cools targets) Battery performance degrades in extreme cold
Ground Sample Distance (GSD) at Operating Altitudes
Thermal GSD vs. Altitude
GSD Formula
GSD = (H x pixel_pitch) / focal_length
Where H = altitude AGL, pixel_pitch = 12 µm, focal_length = 13 mm
| Altitude | GSD | px/cell (~6 in. / 156 mm) | px/cell (~3 in. / 78 mm half-cut) | Illustrative capture-detail tier |
|---|---|---|---|---|
| 49 ft (15m) | 1.4 cm/px | 11.3 | 5.7 | 11.3 px/cell |
| 66 ft (20m) | 1.8 cm/px | 8.5 | 4.2 | 8.5 px/cell |
| 82 ft (25m) | 2.3 cm/px | 6.8 | 3.4 | 6.8 px/cell |
| 98 ft (30m) | 2.8 cm/px | 5.6 | 2.8 | 5.6 px/cell |
| 131 ft (40m) | 3.7 cm/px | 4.2 | 2.1 | 4.2 px/cell |
| 164 ft (50m) | 4.6 cm/px | 3.4 | 1.7 | 3.4 px/cell |
| 197 ft (60m) | 5.5 cm/px | 2.8 | 1.4 | 2.8 px/cell |
| 246 ft (75m) | 6.9 cm/px | 2.3 | 1.1 | 2.3 px/cell |
This table is planning math, not a delivered-resolution promise. The aircraft records 640×512 radiometric thermal data; thermal resolution depends on flight altitude, lens choice, and capture geometry.
Practical Note on Half-Cut Cells
Modern panels increasingly use half-cut cells (~3 in. / 78 mm). These require lower altitudes for the same pixel-per-cell count. At 98 ft (30m) AGL, a half-cut cell gets only ~2.8 pixels across—below the detailed mode threshold. For half-cut-cell planning, lower altitude increases pixel sampling; project geometry and safety constraints determine the flight plan. Pixel counts do not establish an individual-cell diagnosis.
Measurement Distance Constraint
The Autel 640T specifies accurate temperature measurement at 7–65 ft (2–20m) standoff distance. At flight altitudes above 65 ft (20m), absolute temperature readings should be treated as qualitative unless field-validated. For commissioned solar screening, we compare relative surface-temperature differences and document the reference selection. Relative differences (Tdefect - Tref) remain valid at higher altitudes because the atmospheric attenuation affects both measurements equally. Anomalies flagged at altitude are confirmed with low-altitude verification passes when quantitative temperature values are required.
Calibration & Maintenance Schedule
| Activity | Frequency | Method |
|---|---|---|
| Factory Calibration | Annual | Return to manufacturer. Blackbody reference sources, NIST-traceable. Certificate of calibration provided. |
| Field Verification | Quarterly | Check against portable blackbody reference target at known temperatures. Verify reading is within manufacturer's stated accuracy (±3°C or ±3% of reading (whichever greater)). |
| Commissioned-Scope Equipment Checks | As specified in the commissioned checklist | Available checks include NUC (Non-Uniformity Correction), lens-cover cycling, stable-image review, and ambient capture-context notes. |
| Lens Cleaning | As specified in the commissioned equipment checklist | The commissioned checklist can call for visual inspection of the Germanium lens and cleaning with lens-safe solution only when contamination is present; the Ge window is factory-coated and unnecessary contact risks surface damage. Dust, fingerprints, or organic residue on the Ge window degrade thermal transmission and introduce measurement error. |
| Aircraft RTK Status | Before survey capture | Manufacturer RTK state describes camera-position metadata; it does not establish delivered finding accuracy. |
Ask which equipment records are available for your scope. A commissioned deliverable identifies any manufacturer or field records included with that project.
How Documented Field Practices Relate to the Framework's Inspection Topics
Environmental Conditions
The commissioned capture plan defines environmental data-quality gates. We log the applicable conditions before and during the flight and report departures from the plan.
| Inspection topic | Documented project procedure | Verification Method |
|---|---|---|
| Plane-of-array irradiance ≥600 W/m² | Minimum 600 W/m²; preferred ≥700 W/m². Flight aborted if irradiance drops below 600 W/m² for more than 2 minutes. | Irradiance verified via site sensor data or reference irradiance sources, logged with the flight record. |
| Irradiance stability (<10% variation/min) | Flights scheduled during cloud-free windows. Data from intermittent cloud periods flagged and reviewed before inclusion. | Irradiance verified via site sensor data or reference irradiance sources, logged with the flight record. Post-flight QA rejects frames captured during irradiance dips. |
| Wind speed ≤22 mph (10 m/s) | We target ≤11 mph (5 m/s) as the stated data-quality target for this workflow. Wind speed is logged; marginal or aborted conditions are governed by the commissioned capture plan. | On-site anemometer. Wind speeds above 11 mph (5 m/s) are noted as a condition in the report because convective cooling reduces apparent ΔT. |
| Modules under normal operating load | Confirmed with site operator that all strings and inverters are energized before survey begins. Any known offline strings are documented. | Pre-flight coordination with site O&M team. Inverter status logged at survey start. |
Camera & Resolution Requirements
| Inspection characteristic | Equipment specification |
|---|---|
| Radiometric thermal camera | 640x512 radiometric sensor; full per-pixel temperature data stored in R-JPEG format. 14-bit thermal data, not visual-only palette overlay. |
| NETD ≤0.1 K (recommended) | ≤50 mK (0.05 K) manufacturer-listed NETD |
| ≥5x5 px/cell (detailed mode) | Achieved at ≤98 ft (30m) AGL for ~6 in. (156 mm) cells. See GSD table for altitude/resolution tradeoffs. We confirm cell dimensions with the client and select flight altitude accordingly. |
| ≥3x3 px/cell (simplified mode) | Achieved at ≤164 ft (50m) AGL for ~6 in. (156 mm) cells. Used for high-altitude screening passes on large arrays before targeted low-altitude detail passes. |
| View angle ≤60° from perpendicular | We target ≤30° from perpendicular (nadir or near-nadir) to minimize emissivity variation and reflected apparent temperature. Flight path planned to maintain consistent viewing geometry across the array. Module tilt angle factored into flight planning. |
Flight Pattern & Coverage
Systematic Grid Survey
- Pattern: Parallel flight lines aligned with tracker rows or fixed-tilt row orientation
- Forward Overlap: ≥70% (thermal), ≥80% (RGB) — adds repeat observations along the flight path
- Side Overlap: ≥60% (thermal), ≥70% (RGB) — ensures full coverage between adjacent flight lines
- Speed: 7–11 mph (3–5 m/s) depending on altitude and GSD target. Slower speed = less motion blur in thermal frames.
Image Capture
- Trigger: Distance-based (not time-based) to maintain consistent overlap regardless of wind-induced speed variations
- Orientation: Camera nadir (pointing straight down) or tilted to match module plane-of-array angle for perpendicular viewing
- Thermal/RGB relationship: Capture streams are not assumed to be paired at identical timestamps
- Metadata: Available pose and timestamp records are retained and their limits documented
Why High Overlap Matters
Higher forward overlap increases repeat observations where frame coverage overlaps. Reviewers can compare transient artifacts such as passing shadows across adjacent frames, while thermal signatures remain investigation targets for ground verification. Absolute coordinate accuracy is stated only when measured for the project.
Data Processing Pipeline
Ingest & Quality Gate
Raw R-JPEG thermal frames, RGB images, flight logs, and irradiance-source data are ingested. Automated QA rejects frames captured during irradiance dips (<600 W/m²), excessive motion blur, or RTK signal loss. Typically 5-15% of frames are rejected during QA depending on conditions.
Radiometric Orthomosaic Generation
Thermal frames are stitched into a georeferenced orthomosaic using photogrammetric processing. Crucially, this is a radiometric mosaic — the per-pixel temperature values are preserved through the stitching process, not averaged into visual-only palettes. The result is a georeferenced GeoTIFF containing radiometric apparent-temperature data, documented processing, and disclosed quality limits.
Anomaly Detection & Classification
Temperature differences (ΔT) between suspected anomalies and adjacent healthy reference modules are calculated and normalized to 1000 W/m² standard irradiance using the formula:
Observed signatures are labeled by pattern and confidence, then separated as confirmed or suspected for ground verification. Pattern labels are not root-cause diagnoses. See our IEC TS 62446-3 methodology page for the reporting framework and priority bins.
Peer Review & Validation
Every anomaly is manually reviewed against the paired RGB image to confirm physical plausibility. Suspected false positives (bird droppings, temporary shading, reflections) are flagged and downgraded or removed. For suspected transient anomalies, the repeat-frame redundancy from our 70%+ overlap is used to confirm persistence.
Deliverable Generation
Final outputs are generated in multiple formats for different stakeholders. See Deliverable Formats below.
Deliverable Formats
GeoTIFF Thermal Orthomosaic
Georeferenced thermal map of the full site with preserved radiometric data. Compatible with QGIS, ArcGIS, and most asset management GIS systems.
CRS: UTM Zone 14N (EPSG:32614) for orthomosaics; WGS84 (EPSG:4326) for point data
CSV Anomaly Log
Row-level defect records with GPS coordinates, normalized ΔT, severity classification, anomaly type, and image references. Designed for direct import into CMMS platforms.
See CSV schema documentation for field definitions.
KML/KMZ Field Maps
Pin-drop anomaly locations color-coded by severity. Designed for field crew tablets. Tap a pin to see anomaly type, ΔT, severity, and a thermal thumbnail.
Compatible with Google Earth, Avenza Maps, and standard GPS navigation apps
PDF Inspection Report
Human-readable report with executive summary, findings by severity, thermal+RGB image pairs for each anomaly, and inspection conditions metadata. Format varies by service tier.
Enterprise tier includes a documented project-method appendix with available calibration records.
Data Interoperability
All deliverables use open, standard formats. No proprietary viewer required. For integration with specific asset management platforms (PowerFactors, Raptor Maps, etc.), we can adjust field mappings and export schemas. See our data interoperability page for details.
Quality Assurance
Every inspection passes through these QA gates before deliverables are released to the client.
Environmental-condition record: Irradiance verified via site sensor data or reference irradiance sources, logged with the flight record. Wind speed, ambient temperature, and cloud conditions logged.
Spatial coverage: Orthomosaic checked against site plan for gaps. Any uncovered areas noted in the report with reason (access restriction, tracker in stow, etc.).
RTK positioning: RTK Fix percentage for the survey is reported. Frames captured during RTK Float or standalone GPS mode are flagged with degraded position accuracy.
False positive review: Every flagged anomaly verified against RGB imagery and repeat frames. Transient artifacts removed. Borderline cases are included with a reduced confidence notation rather than silently dropped.
Normalization check: ΔT values are spot-checked against raw radiometric data to confirm normalization formula was applied correctly. Reference temperature selection is checked against the documented project method and the selected comparison modules are recorded.
Accuracy Disclosure
Temperature measurement accuracy: ±3°C or ±3% of reading (whichever greater), valid within a −20°C to +60°C environment; accurate measurement distance 2–20 m.
IEC 62446-3 anomaly classifications assume ≥600 W/m² plane-of-array irradiance with stable conditions
Temperature measurement accuracy: ±3°C or ±3% of reading (whichever greater), valid within −20°C to +60°C environment
Quantitative readings assume 2–20 m measurement distance; beyond this, treat values as qualitative
What This Means for Your Reports
Our defect classification relies on relative temperature differences (ΔT between anomaly and reference), not absolute temperature readings. Relative measurements are more robust than absolute values because atmospheric and environmental effects largely cancel out. The High Thermal Sensitivity absolute accuracy specification is relevant for specific engineering analyses (e.g., comparing measured module temperature to modeled predictions) but does not directly affect ΔT-based anomaly classification.
Related Technical Resources
- IEC TS 62446-3 Methodology — Anomaly classification, severity bins, ΔT normalization, and CSV schema
- Solar Inspection Services — Service tiers, deliverables, and pricing for utility-scale solar
- Equipment Overview — General equipment capabilities and professional certifications
- Thermal Drone Inspection Guide — How infrared cameras work, radiometric vs. non-radiometric, and cost estimator
- Solar Panel Inspection Guide — Defect types, inspection methodology, and energy loss calculator
- Data Interoperability — Deliverable formats, GIS compatibility, and CMMS integration
Questions About Our Equipment or Methodology?
We welcome technical questions from solar engineers, asset managers, and procurement teams. If you want to see sample deliverables or discuss how our methodology applies to your specific site configuration, reach out.
Based in Hale Center, TX. Serving the Texas Panhandle, South Plains, and ERCOT footprint. No travel fees within 40 miles.