SHOALS - Technical Overview and Specifications
Airborne laser bathymetry relies on the differential timing of laser pulses reflected from the water surface and the underwater surface, to determine the water depth at the point where the laser pulses strike the water surface.
The integrated SHOALS sensor and processing systems implement this simple strategy accurately and robustly, maximizing utility for marine surveying. |
Transceiver
The SHOALS laser generates short pulses of light at two wavelengths: infrared and blue-green.
The infrared pulse is reflected by the water surface.
The blue-green pulse penetrates the water and is reflected from the bottom.
Airborne Operation
The laser scans beneath the aircraft, sending out pulses in a swath over which the position of the water surface and sea floor is measured.
To correct for the aircraft's movements, the motion of the aircraft is measured by an inertial reference system (IRS). This data is used for real-time pitch and roll compensation, and recorded for post-processing, while a GPS receiver records the aircraft's position. A geo-referenced digital camera records the area being surveyed.
The laser pulse, waveforms, scan angle, GPS data and IRS data are combined to produce accurate real-time and post-processed sounding positions or terrain elevations.
The raw SHOALS sensor data collected by the airborne system is stored on mirrored removable hard drives, along with mission planning information and mission log information.
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SHOALS-3000 |
SHOALS-1000 |
| Hydrographic mode |
| Measurement rate |
3,000 Hz |
1,000 Hz |
| Operating altitude |
300-400 m (for maximum depth) |
200-400 m (for maximum depth) |
| Depth measurement accuracy |
IHO Order 1 (25 cm, 1 σ) |
IHO Order 1 (25 cm, 1 σ) |
| Horizontal accuracy |
IHO Order 1 (25 cm, 1 σ) |
IHO Order 1 (25 cm, 1 σ) |
| Minimum depth |
0.2 m |
0.2 m |
| Maximum depth |
50 m |
50 m |
| Sounding density |
2x2, 3x3, 4x4, 5x5 m |
2x2, 3x3, 4x4, 5x5 m |
| Swath width |
Variable, up to 0.75 x altitude |
Variable, up to 0.58 x altitude |
| Typical swath width |
300 m (@ 4x4 m) |
215 m (@ 4x4 m) |
| Typical aircraft speed |
125 - 260 knots |
125 - 260 knots |
| Eyesafe altitude |
150 m |
150 m |
| Power requirements |
70 A @ 28 VDC |
60 A @ 28 VDC |
| Operating temperature |
5 - 40°C |
5 - 40°C |
| Storage temperature |
-20 - +60°C |
-20 - +60°C |
| Humidity |
0 - 95% non-condensing |
0 - 95% non-condensing |
| Laser classification |
Class IV laser product (US FDA 21 CFR 1040)(IEC 60825-1 Ed.1.2) |
Class IV laser product (US FDA 21 CFR 1040)(IEC 60825-1 Ed.1.2) |
| Compliance |
Airworthiness certified to RTCA DO-160D standard |
Airworthiness certified to RTCA DO-160D standard |
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| Optional topographic mode |
| Measurement rate |
20 kHz |
10 kHz |
| Operating altitude |
300-1000 m |
300-700 m |
| Horizontal accuracy |
2.0 m, 1 σ, DGPS 2/1000 x altitude, KGPS |
2.0 m, 1 σ, DGPS 2/1000 x altitude, KGPS |
| Vertical accuracy |
25 cm, 1 σ |
25 cm, 1 σ |
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| Airborne system dimensions and weights |
| Sensor |
70 W x 60 D x 60 H cm; 77 kg |
70 W x 60 D x 60 H cm; 72 kg |
| Operator rack |
53 W x 73 D x 62 H cm; 55 kg |
53 W x 73 D x 62 H cm; 55 kg |
| Chiller rack** |
53 W x 60 D x 44 H cm; 40 kg |
53 W x 65 D x 44 H cm; 40 kg |
| Laser rack** |
53 W x 60 D x 49 H cm; 45 kg |
53 W x 60 D x 44 H cm; 42 kg |
Specifications subject to change without notice
** Chiller and laser racks can be stacked
