A 10-nm Spectral Resolution Hyperspectral LiDAR System Based on an Acousto-Optic Tunable Filter
<p>Schematic setup of acousto-optic tunable filter based hyperspectral lidar (AOTF-HSL).</p> "> Figure 2
<p>Calibration of AOTF-HSL.</p> "> Figure 3
<p>Range measurements of the AOTF-HSL from 650 nm to 1000 nm on 4 standard targets with different reflectivity.</p> "> Figure 4
<p>Output of the SVC<sup>®</sup> spectrometer by modifying the transmission power of the supercontinuum laser (SCL) source from 10–100% with a 10% step length at 720 nm on a white reflectance standard with 99% reflectivity.</p> "> Figure 5
<p>Relationship between AOTF-HSL measurement and spectrometer measurement in selected NIR bands.</p> "> Figure 6
<p>Four plants under test: (<b>a</b>) aloe with yellow and green leaves, (<b>b</b>) dracaena with yellow and green leaves, (<b>c</b>) balata and (<b>d</b>) radermachera.</p> "> Figure 7
<p>Hyperspectral Lidar derived spectral profiles of 6 leaves from 4 plant species (dracaena, aloe, balata, and radermachera).</p> "> Figure 8
<p>HSL derived spectral profile of green leaves from (<b>a</b>) dracaena (<b>b</b>) aloe, (<b>c</b>) balata (<b>d</b>) radermachera compared with spectrometer measurements.</p> "> Figure 9
<p>HSL derived spectral profile of yellow leaves from (<b>a</b>) dracaena, (<b>b</b>) aloe compared with spectrometer measurements.</p> "> Figure 10
<p>Scatter diagrams of the reflectance of green leaf cases measured by AOTF-HSL and SVC spectrometer.</p> "> Figure 11
<p>Scatter diagrams of the reflectance of yellow leaf cases measured by AOTF-HSL and SVC spectrometer.</p> ">
Abstract
:1. Introduction
- (1)
- The AOTF-HSL solution is proposed, designed, and tested in laboratory conditions. The designed AOTF-HSL operates on a spectrum range from 500 nm to 1000 nm with a 10 nm spectral resolution. The instrument represents an advancement related to previous similar instruments in allowing genuinely hyperspectral (continuous) data to be generated rather than discrete multispectral data. The new system also represents a significant advance in terms of the number of channels available. The laser emission unit consists of an SCL and an AOTF device, ensuring that different wavelengths of the laser beam can be emitted at each time slot. This design allows continuous wavelength selection of the laser pulse in the time dimension and also the filtered pulse at the exit of the transmitted component for better eye safety. Additionally, such a time-multiplexing solution is different with spectrograph based HSL.
- (2)
- Distance measurement capabilities are marginally addressed with a basic demonstration and simple precision assessment. The range precision or range stability over 51 spectral channels of the AOTF-HSL is preliminarily evaluated with a simple test case, four standard reflection boards (100%, 70%, 40%, and 20%) placed at a measured distance of 37.5 meters, and the random range errors can be observed.
- (3)
- In order to precisely calibrate the HSL intensity, the corresponding relationship between the target attribute and the output waveform of HSL is determined based on analysis of the radiation transmission mechanism of HSL, and the calibration model and method are constructed for more accurate quantitative applications of HSL. LiDAR calibration can be achieved by passing a sample of the transmitted signal through the receiver and monitoring the signal from the standard targets both from a spectrometer and the HSL. The calibration tests are conducted using different standard diffuse reflectors (99%, 70%, 40%, 20%, and 5%).
- (4)
- The AOTF-HSL application to agriculture is verified by various vegetation experiments. The spectral profiles of green and yellow leaves from four species are analyzed. The calibrated AOTF-HSL experimental results are also compared with the corresponding measurements from a standard spectrometer (SVC© HR-1024) (hereinafter referred to as the SVC spectrometer). The average spectral difference (absolute value) of the six leaf samples are minor, i.e., 1.37% (green leaf of dracaena), 8.79% (yellow leaf of dracaena), 0.84% (green leaf of aloe), 4.6% (yellow leaf of aloe), 1.36% (green leaf of balata), and 0.77% (green leaf of radermachera), indicating that the AOTF-based high spectral resolution HSL is effective for this application. The results reveal that the potential of this active remote sensing is applicable for vegetation research.
2. Methods
3. Tests and Calibration
3.1. Range Precision Test
3.2. Spectral Profile Test
3.3. Calibration of the Spectral Profile
4. Results and Discussion
4.1. Range Precision Evaluation
4.2. Spectral Profile Calibration
4.3. Spectral Profiles
5. Conclusions
Author Contributions
Acknowledgments
Conflicts of Interest
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Parameter | |
---|---|
Spectral range | 430–1450 nm |
Spectral resolution | 2–10 nm |
Output efficiency | >40% |
Polarization | Line polarization |
Beam divergence | 0.4 mill radian |
Beam diameter (at exit) | 10 mm |
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Chen, Y.; Li, W.; Hyyppä, J.; Wang, N.; Jiang, C.; Meng, F.; Tang, L.; Puttonen, E.; Li, C. A 10-nm Spectral Resolution Hyperspectral LiDAR System Based on an Acousto-Optic Tunable Filter. Sensors 2019, 19, 1620. https://doi.org/10.3390/s19071620
Chen Y, Li W, Hyyppä J, Wang N, Jiang C, Meng F, Tang L, Puttonen E, Li C. A 10-nm Spectral Resolution Hyperspectral LiDAR System Based on an Acousto-Optic Tunable Filter. Sensors. 2019; 19(7):1620. https://doi.org/10.3390/s19071620
Chicago/Turabian StyleChen, Yuwei, Wei Li, Juha Hyyppä, Ning Wang, Changhui Jiang, Fanrong Meng, Lingli Tang, Eetu Puttonen, and Chuanrong Li. 2019. "A 10-nm Spectral Resolution Hyperspectral LiDAR System Based on an Acousto-Optic Tunable Filter" Sensors 19, no. 7: 1620. https://doi.org/10.3390/s19071620
APA StyleChen, Y., Li, W., Hyyppä, J., Wang, N., Jiang, C., Meng, F., Tang, L., Puttonen, E., & Li, C. (2019). A 10-nm Spectral Resolution Hyperspectral LiDAR System Based on an Acousto-Optic Tunable Filter. Sensors, 19(7), 1620. https://doi.org/10.3390/s19071620