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Multi-wavelength airborne laser scanning ILMF 2011, New Orleans Dr. Andreas Ullrich CTO, RIEGL LMS GmbH.

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Presentation on theme: "Multi-wavelength airborne laser scanning ILMF 2011, New Orleans Dr. Andreas Ullrich CTO, RIEGL LMS GmbH."— Presentation transcript:

1 Multi-wavelength airborne laser scanning ILMF 2011, New Orleans Dr. Andreas Ullrich CTO, RIEGL LMS GmbH

2 contents introduction: components of ALS systems full waveform analysis vs. online waveform processing primary and secondary ALS data products discussion multi-spectral, hyper-spectral, multi-wavelength selection criteria for laser wavelength availability of laser sources target properties signal attenuation, background radiation laser safety classification of multi-wavelength data / systems conclusions

3 components of ALS systems RIEGL LMS-Q680i RIEGL DR-680 RiPROCESS IMU & GPS Flight Guidance RiACQUIRE DA42-MPP RIEGL VQ-580 RIEGL VQ-820-G

4 R A W Q-560/Q-680i state-of-the-art echo waveform digitizing systems Full Waveform analysis range: R [m] amplitude: A [LSB and linearized] echo width: W [ns] On-Line Waveform Processing range: R [m] calibrated amplitude: A [dB] calibrated reflectance: r [dB] pulse shape deviation: dev [1] R A RIEGL VQ-580 dev RIEGL VQ-820-G

5 RIEGL LMS-Q680i, wavelength 1550 nm dry conditionswet snow primary data: point cloud

6 RIEGL VQ-580 wavelength 1064 nm amplitude in dB above detection threshold RIEGL VQ-580 wavelength 1064 nm reflectance in dB above white diffusely reflecting target RIEGL VQ-580 wavelength 1064 nm pulse shape deviation from expected pulse shape

7 images at different wavelengths 1064 nmvisible 1550 nm532 nm visible 532 nm 1064 nm 1550 nm

8 radiometric calibration Radiometric calibration of small-footprint airborne laser scanner measurements: Basic physical concepts, Wagner, W., ISPRS Journal of Photogrammetry and Remote Sensing, 65, Laser Radar Cross Section (LRCS) cross section  in [m²] area-normalized cross section values in [m²m -2 ] or [dB] by laser footprint area:  by illuminated object area:  0 actual geometric cross- section of target interacting with laser beam reflectance directivity of backscattered reflection

9 radiometric calibration

10 multispectral/hyperspectral imaging vs. multi-wavelength ALS 400 nm800 nm1200 nm1600 nm multispectral imaging hyperspectral imaging hyperspectral lidar supercontinuum laser (500 nm – 2400 nm) array of receiver channels and ROIC multi- wavelength lidar 532 nm905 nm1064 nm1550 nm

11 wavelength selection criteria for ALS sensors pulsed time-of-flight laser ranging: best performance wrt maximum range, measurement speed, ranging precision and accuracy selection of wavelength availability of suitable laser and detector reflectance of objects attenuation of atmosphere and background radiation laser safety laser requirements short pulse width (multi-target resolution, high precision) high peak power (maximum range) good beam quality (beam divergence, spatial resolution) high pulse repetition rate (point density) narrow spectral width (background rejection) detector requirements high bandwidth (corresponds to pulse width) high sensitivity (maximum range) low noise (high precision)

12 UV INFRARED diode lasers, 905 nm solid state lasers (fundamental wavelength), Nd:YAG, 1064 nm solid state lasers (harmonics), Nd:YAG, 532 nm, (355 nm) fiber lasers, Er-doped, 1.55 µm fiber lasers, Yt-doped, 1.06 µm fiber lasers, Ho-doped, 2.05 µm frequency-doubled fiber lasers, 532 nm suitable laser sources 532 nm355 nm 1550 nm2050 nm1064 nm532 nmfiber 905 nmdiode 1064 nmsolid state

13 target reflectance versus wavelength 532 nm 905 nm 1064 nm 1550 nm wavelength [µm] relative reflectance [%]

14 background radiation versus wavelength solar spectral irradiance at zenith sun angle 60° at sea level corresponds to spectrum of sun light absorption due to ozone (O 3 ), water vapor (H 2 O), oxygen (O 2 ), carbon dioxide (C0 2 ) wavelength [µm] solar irradiance [W/m²µm] 532 nm 1064 nm 905 nm 1550 nm

15 atmospheric attenuation versus wavelength wavelength [µm] transmittance [%] transmittance of 1000 feet horizontal air path (sea level) atmospheric transmission 20 km, one way visibility 23 km, 10 km, 5 km 532 nm 1064 nm 905 nm 1550 nm

16 wavelength [µm] absorption coefficient [cm -1 ] visibleinfraredultraviolet attenuation in water versus wavelength absorption coefficient of clear seawater attenuation at depth 10 m attenuation at depth 0.1 m attenuation at depth 1 mm 0.1 dB 1 dB 10 dB 0.01 dB 100 dB 53 dB0.53 dB 50 dB 10 dB 100 dB 1 dB 0.1 dB 1 dB 10 dB 100 dB 0.01 dB 3.8 dB dB

17 laser safety considerations MPE: maximum permissible exposure parameter: exposure duration / pulse width 1550 nm 1064 nm 905 nm 532 nm 355 nm

18 NOHD, eNOHDNOHD eNOHD NOHD eNOHD Laser Classes / NOHD / ENOHD Laser Safety Standards NOHD (nominal ocular hazard distance): distance beyond which exposure becomes less than maximum permissible exposure (MPE) extended NOHD: includes the possibility of optically-aided viewing max. reflectance 20% max. reflectance 80% RIEGL LMS- 80kHz 1.5m Range [m] 0m 10m 2000m RIEGL 50kHz 15m 105m 2000m EN CFR class 1 class I class 1M- class 2 class II class 2M - class 3R class IIIA class 3B class IIIB class 4 class IV RIEGL 100kHz 80m 500m 2000m 1600m

19 classification of multi-wavelength ALS descriptionsame area common platform common scanner same IFOV synchron ized pulses data set from two different campaigns X data from several laser scanners on same platform XX several LIDARs sharing the same scanner XXX co-axial beams having thus the same instantaneous field-of-view XXXX additionally pulses of LIDARs are synchonized XXXXX increasing sensor/system complexity increasing flexibility

20 conclusions select scanner model (wavelength) according to target characteristics, mission requirements, laser safety requirements,...  wide variety of applications covered by eye-safe 1550 nm ALS scanners (e.g., RIEGL LMS-680i and RIEGL VQ-480) for special applications, e.g., forest health investigations integrate two or more scanners with different wavelength on a single platform  providing flexible “multi-wavelength” system (e.g., RIEGL VQ-480 at 1550 nm and RIEGL VQ-580 at 1064 nm) for hydrography, ad 532 nm LIDAR regardless of wavelength: echo-digitizing pulsed time-of-flight systems provide utmost accuracy, multi-target resolution and calibrated (calibratable) amplitudes and target’s cross-section

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