The laser beam is able to accurately measure the range between the sensor and the ground with a scanning motion across the flight path of the aircraft.
The systems are: the ALTM 3033, the ALTM 3100 EA and the Gemini, produced by Optech in Toronto (Canada).
Technical features:
| ALTM 3033 | ALTM 3100EA | Gemini | |
Operating altitude |
265 - 3000 m |
80 - 3500 m nominal |
150 - 4000 |
Elevation accuracy * |
15 cm < 1200 m (1 sigma) 25 cm < 2000 m (1 sigma) 35 cm < 3000 m (1 sigma) |
15 cm < 1200 m (1 sigma) 25 cm < 2000 m (1 sigma) 35 cm < 3000 m (1 sigma) |
10 cm < 1000 m (1 sigma) 15 cm < 2000 m (1 sigma) 20 cm < 3000 m (1 sigma) |
Horizontal accuracy * |
1/2000 x flying altitude (1 sigma) |
1/2000 x flying altitude (1 sigma) |
1/5.500 x flying altitude (1 sigma) |
Range resolution |
1 cm |
1 cm |
1 cm |
Scan angle |
Variable from 0 to ±20 |
Variable from 0 to ±25 |
Variable from 0 to ±25 |
Swath width |
Variable from 0 m to 0.68 x altitude |
Variable from 0 m to 0.93 x altitude |
Variable from 0 m to 0.93 x altitude (m) |
Angular resolution |
0.01° |
0.01° |
0.01° |
Scan frequency |
Varies with scan angle |
Variable, maximum 70 Hz |
Variable, maximum 70 Hz |
Laser wavelength |
1064 nm |
1064 nm |
1064 nm |
Laser repetition rate |
33 kHz |
33 kHz (max. altitude AGL 3500 m) 50 kHz (max. altitude AGL 2500 m) 70 kHz (max. altitude AGL 1700 m) 100 kHz (max. altitude AGL 1100 m) |
33 kHz (max. altitude AGL 4000 m) 50 kHz (max. altitude AGL 3000 m) 70 kHz (max. altitude AGL 2500 m) 100 kHz (max. altitude AGL 2000 m) 125 kHz (max. altitude AGL 1600 m) 142 kHz (max. altitude AGL 1400 m) 167 kHz (max. altitude AGL 1200 m) |
Beam divergence |
Variable: 0.8 mrad or 0.2 mrad (1/e) nominal |
Variable: 0.26 mrad (1/e) o 0.85 mrad (1/e ) |
Doppia 0.3 mrad (1/e) e 0.8 mrad (1/e) |
“Eye safe” altitude limit |
175 m @ 0.8 mrad 650 m @ 0.2 mrad |
80 m @ 0.85 mrad 1500 m @ 0.26 mrad |
80 m @ 0.80 mrad 400 m @ 0.26 mrad |
Intensity |
Measurement of intensity of each pulse received |
Measurement of intensity of each pulse received |
intensità di ogni impulso ricevuto Range dinamico a 12 bit per ogni singolo impulso ricevuto |
Collected data |
Simultaneous measurement in range of first and last pulse |
Simultaneous measurement in range of first and last pulse for each pulse emitted |
Simultaneous measurement in range of first and last pulse for each pulse emitted |
Laser classification |
Class IV laser products (FDA CFR 21) |
Class IV laser products (FDA CFR 21) |
Class IV laser products (FDA CFR 21) |
GPS receiver |
Internal Novatel Millenium DL |
Internal Novatel Millenium DL |
Trimble MS750 |
Power requirements |
28 VDC @35 A peak |
28 VDC @35 A peak |
28 VDC @45 A peak |
Operating temperature |
15-35 °C |
-10 / +50°C |
-10 / +50°C |
Humidity |
0-95 % non- condensing |
0-95 % non-condensing |
0-95 % non-condensing |
* To meet its specified accuracy, the ALTM must receive GPS data of sufficient quality and satisfy the following conditions:
At least 4 satellites are continually tracked by the receiver during the survey
Satellite elevation is above the horizon > 15°
Good satellite geometry (PDOP < 4)
Aircraft stays within 30km of the GPS base station
If one of the conditions is not met or if any external source of electromagnetic radiation interferes with the GPS signals, the accuracy of the ALTM as defined above can not be guaranteed.
Helica uses the following GPS collection parameters:
Simultaneous visibility of at least 6 satellites
Satellite elevations: greater than 15° above the horizon
PDOP < 3
GPS ground station always within 30 km of helicopter.
