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

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 contents

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

state-of-the-art echo waveform digitizing systems RIEGL VQ-820-G R A W R A RIEGL VQ-580 Q-560/Q-680i dev 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] state-of-the-art echo waveform digitizing systems

primary data: point cloud RIEGL LMS-Q680i, wavelength 1550 nm dry conditions wet snow primary data: point cloud

primary data: point cloud RIEGL VQ-580 wavelength 1064 nm pulse shape deviation from expected pulse shape RIEGL VQ-580 wavelength 1064 nm reflectance in dB above white diffusely reflecting target RIEGL VQ-580 wavelength 1064 nm amplitude in dB above detection threshold primary data: point cloud

images at different wavelengths 1064 nm visible visible 532 nm 1064 nm 1550 nm 1550 nm 532 nm images at different wavelengths

radiometric calibration 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 Radiometric calibration of small-footprint airborne laser scanner measurements: Basic physical concepts, Wagner, W., ISPRS Journal of Photogrammetry and Remote Sensing, 65, 2010. radiometric calibration

radiometric calibration

multispectral/hyperspectral imaging vs. multi-wavelength ALS 400 nm 800 nm 1200 nm 1600 nm multispectral imaging hyperspectral imaging multi- wavelength lidar 532 nm 905 nm 1064 nm 1550 nm hyperspectral lidar supercontinuum laser (500 nm – 2400 nm) array of receiver channels and ROIC multispectral/hyperspectral imaging vs. multi-wavelength ALS

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) airborne laser scanning makes use of pulsed time-of-flight laser ranging (best figure of merit taking into account maximum range, measurement speed, ranging precision and accuracy) traditionally high-power mid-pulse-repetition rate monochromatic sources in use selection of wavelength governed by availability of suitable laser and detector, but also by reflectance of objects, attenuation of atmosphere and background radiation, laser safety requirements on laser: 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), etc. requirements on detector: high bandwidth (corresp. pulse width), high sensitivity (max. range), etc. wavelength selection criteria for ALS sensors

solid state lasers (fundamental wavelength), Nd:YAG, 1064 nm 200 400 600 800 1000 1200 1400 1600 1800 2000 UV INFRARED diode 905 nm solid state 355 nm 532 nm 1064 nm fiber 532 nm 1064 nm 1550 nm 2050 nm 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

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

background radiation versus wavelength solar spectral irradiance at zenith sun angle 60° at sea level 1400 corresponds to spectrum of sun light absorption due to ozone (O3) , water vapor (H2O), oxygen (O2), carbon dioxide (C02) 1200 532 nm 1000 800 solar irradiance [W/m²µm] 600 1064 nm 400 905 nm 1550 nm 200 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 wavelength [µm] background radiation versus wavelength

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

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 0.2 0.4 0.6 0.8 1.0 2.0 4.0 6.0 8.0 10 wavelength [µm] absorption coefficient [cm-1] 10 000 1 000 100 10 1 0.1 0.01 0.001 0.0001 visible infrared ultraviolet 0.1 dB 1 dB 10 dB 0.01 dB 100 dB 53 dB 0.53 dB 50 dB 10 dB 100 dB 1 dB 0.1 dB 0.01 dB 3.8 dB 0.038 dB attenuation in water versus wavelength

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

Laser Classes / NOHD / ENOHD RIEGLLMS-Q680i @ 80kHz RIEGL VQ-580 @ 50kHz RIEGL VQ-820-G @ 100kHz Laser Safety Standards NOHD, eNOHD NOHD eNOHD NOHD eNOHD EN60825 21CFR1040.10 class 1 class I class 1M - class 2 class II class 2M class 3R class IIIA class 3B class IIIB class 4 class IV 0m 1.5m 15m 80m 10m 105m 500m 1600m 1600m 1600m max. range @ reflectance 20% 2000m 2000m 2000m Range [m] max. range @ reflectance 80% 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 Laser Classes / NOHD / ENOHD

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

for hydrography, ad 532 nm LIDAR 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 conclusions