Analysis and Radiometric Calibration for Backscatter Intensity of Hyperspectral LiDAR Caused by Incident Angle Effect

Hyperspectral LiDAR (HSL) is a new remote sensing detection method with high spatial and spectral information detection ability. In the process of laser scanning, the laser echo intensity is affected by many factors. Therefore, it is necessary to calibrate the backscatter intensity data of HSL. Laser incidence angle is one of the important factors that affect the backscatter intensity of the target. This paper studied the radiometric calibration method of incidence angle effect for HSL. The reflectance of natural surfaces can be simulated as a combination of specular reflection and diffuse reflection. The linear combination of the Lambertian model and Beckmann model provides a comprehensive theory that can be applied to various surface conditions, from glossy to rough surfaces. Therefore, an adaptive threshold radiometric calibration method (Lambertian–Beckmann model) is proposed to solve the problem caused by the incident angle effect. The relationship between backscatter intensity and incident angle of HSL is studied by combining theory with experiments, and the model successfully quantifies the difference between diffuse and specular reflectance coefficients. Compared with the Lambertian model, the proposed model has higher calibration accuracy, and the average improvement rate to the samples in this study was 22.67%. Compared with the results before calibration with the incidence angle of less than 70°, the average improvement rate of the Lambertian–Beckmann model was 62.26%. Moreover, we also found that the green leaves have an obvious specular reflection effect near 650–720 nm, which might be related to the inner microstructure of chlorophyll. The Lambertian–Beckmann model was more helpful to the calibration of leaves in the visible wavelength range. This is a meaningful and a breakthrough exploration for HSL.

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Radiometric Calibration for Incidence Angle, Range and Sub-Footprint Effects on Hyperspectral LiDAR Backscatter Intensity

Remote Sensing ◽

10.3390/rs12172855 ◽

2020 ◽

Vol 12 (17) ◽

pp. 2855

Author(s):

Changsai Zhang ◽

Shuai Gao ◽

Wang Li ◽

Kaiyi Bi ◽

Ni Huang ◽

...

Keyword(s):

Near Infrared ◽

Spatial Information ◽

Incidence Angle ◽

Incident Angle ◽

Calibration Method ◽

Correction Method ◽

Intensity Data ◽

Radiometric Calibration ◽

Backscatter Intensity ◽

Reference Target

Terrestrial hyperspectral LiDAR (HSL) sensors could provide not only spatial information of the measured targets but also the backscattered spectral intensity signal of the laser pulse. The raw intensity collected by HSL is influenced by several factors, among which the range, incidence angle and sub-footprint play a significant role. Further studies on the influence of the range, incidence angle and sub-footprint are needed to improve the accuracy of backscatter intensity data as it is important for vegetation structural and biochemical information estimation. In this paper, we investigated the effects on the laser backscatter intensity and developed a practical correction method for HSL data. We established a laser ratio calibration method and a reference target-based method for HSL and investigated the calibration procedures for the mixed measurements of the effects of the incident angle, range and sub-footprint. Results showed that the laser ratio at the red-edge and near-infrared laser wavelengths has higher accuracy and simplicity in eliminating range, incident angle and sub-footprint effects and can significantly improve the backscatter intensity discrepancy caused by these effects.

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ScanSAR Mode Sea Ice Image Segmentation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.709.675 ◽

2013 ◽

Vol 709 ◽

pp. 675-678 ◽

Cited By ~ 1

Author(s):

Wen Hui Lang ◽

Can Can Chang ◽

Xue Zhi Yang ◽

Zhang Jie ◽

Jun Min Meng

Keyword(s):

Sea Ice ◽

Large Scale ◽

Incidence Angle ◽

Incident Angle ◽

Speckle Noise ◽

Image Features ◽

Automatic Interpretation ◽

Angle Effect ◽

Main Factors ◽

Regional Clustering

Non-stationary nature of the SAR image is a major obstacle to the automatic interpretation of SAR sea ice image. Incidence angle effect is one of the main factors leading to instability in the sea ice image features. Wide observation with automatic interpretation of SAR sea ice image,incidence angle effect on sea ice region, considering the speckle noise, the incidence angle effect and uncertainties, to the region through the pixel and then to large-scale regional a way, the merger of the incident angle effect correction on the scale of the regional clustering, class and regional operating combination of up to improve the segmentation algorithm for non-stationary adaptability.

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Potential of the Incidence Angle Effect on the Radiometric Calibration of Full-Waveform Airborne Laser Scanning in Urban Areas

American Journal of Remote Sensing ◽

10.11648/j.ajrs.20130104.12 ◽

2013 ◽

Vol 1 (4) ◽

pp. 77 ◽

Cited By ~ 1

Author(s):

Fanar Mansour Abed

Keyword(s):

Urban Areas ◽

Laser Scanning ◽

Incidence Angle ◽

Airborne Laser Scanning ◽

Radiometric Calibration ◽

Full Waveform ◽

Airborne Laser ◽

Angle Effect

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Analyzing the Angle Effect of Leaf Reflectance Measured by Indoor Hyperspectral Light Detection and Ranging (LiDAR)

Remote Sensing ◽

10.3390/rs12060919 ◽

2020 ◽

Vol 12 (6) ◽

pp. 919 ◽

Cited By ~ 2

Author(s):

Peilun Hu ◽

Huaguo Huang ◽

Yuwei Chen ◽

Jianbo Qi ◽

Wei Li ◽

...

Keyword(s):

Hyperspectral Imaging ◽

Near Infrared ◽

Specular Reflection ◽

Incident Angle ◽

Light Detection And Ranging ◽

Light Detection ◽

Leaf Reflectance ◽

Data Registration ◽

Angle Effect ◽

Laser Pulse Intensity

Hyperspectral light detection and ranging (LiDAR) (HSL) combines the characteristics of hyperspectral imaging and LiDAR techniques into a single instrument without any data registration. It provides more information than hyperspectral imaging or LiDAR alone in the extraction of vegetation physiological and biochemical parameters. However, the laser pulse intensity is affected by the incident angle, and its effect on HSL has not yet been fully explored. It is important for employing HSL to investigate vegetation properties. The aim of this paper is to study the incident angle effect of leaf reflectance with HSL and build a model about this impact. In this paper, we studied the angle effect of leaf reflectance from indoor HSL measurements of individual leaves from four typical tree species in Beijing. We observed that (a) the increasing of incident angle decreases the leaf reflectance; (b) the leaf spectrum observed by HSL from 650 to 1000 nm with 10 nm spectral resolution (36 channels) are consistent with those that measured by Analytica Spectra Devices (ASD) spectrometer (R2 = 0.9472 ~ 0.9897); (c) the specular reflection is significant in the red bands, and clear non-Lambertian characteristics are observed. In the near-infrared, there is little specular reflection, but it follows the Lambert-scattering law. We divided the whole band (650–1000 nm) into six bands and established an empirical model to correct the influence of angle effect on the reflectance of the leaf for HSL applications. In the future, the calibration of HSL measurements applied for other targets will be studied by rigorous experiments and modelling.

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Dynamic Cosine Method for Normalizing Incidence Angle Effect on C-band Radar Backscattering Coefficient for Maize Canopies Based on NDVI

Remote Sensing ◽

10.3390/rs13152856 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2856

Author(s):

Zhuangzhuang Feng ◽

Xingming Zheng ◽

Lei Li ◽

Bingze Li ◽

Si Chen ◽

...

Keyword(s):

Land Surface ◽

Dynamic Method ◽

Incidence Angle ◽

Incident Angle ◽

Real Life ◽

Accuracy Evaluation ◽

Backscattering Coefficient ◽

Dynamic Framework ◽

Land Surface Parameter ◽

Angle Effect

Wide mode SAR images have an apparent incidence angle effect. The existing incident angle normalization methods assume that the relationship between the incident angle (θ) and the backscattering coefficient (σPQ) does not change with the growth stage of crops, which is in conflict with the real-life situation. Therefore, the normalization results of σPQ based on these existing methods will affect the accuracy of object classification, target recognition, and land surface parameter inversion. Here, the change in θ-σPQ relationship was investigated based on time-series (April to October) σPQ of maize canopies in northeast China, and a dynamic method based on normalized difference vegetation index (NDVI) was developed to normalize the effect of θ on σPQ. Through the accuracy evaluation, the following conclusions are obtained: (1) the dependence (referring to N) of Sentinel 1 C-band σPQ on θ varies with maize NDVI. In addition, the value of N changed from 9.35 to 0.66 at VV polarization from bare soil to biomass peak, and from 6.26 to 0.99 at VH polarization; (2) a dynamic method was proposed to quantify the change of N based on its strong correlation with NDVI, indicated by R2 of 0.82 and 0.80 for VV and VH polarization, respectively; and (3) the overall root mean square error of normalized σPQ based on the newly-developed dynamic method is 0.51 dB, and this accuracy outperforms the original first-order cosine method (1.37 dB) and cosine square law method (1.08 dB) by about 63% and 53% on the whole. This study provides a dynamic framework for normalizing radar backscatter coefficient, improving the retrieval accuracy of land surface parameters from radar remote sensing.

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Vicarious Radiometric Calibration of Ocean Color Bands for FY-3D/MERSI-II at Lake Qinghai, China

Sensors ◽

10.3390/s21010139 ◽

2020 ◽

Vol 21 (1) ◽

pp. 139

Author(s):

Shengli Chen ◽

Xiaobing Zheng ◽

Xin Li ◽

Wei Wei ◽

Shenda Du ◽

...

Keyword(s):

Infrared Imaging ◽

Large Deviation ◽

Ocean Color ◽

Calibration Method ◽

Surface Measurement ◽

Radiometric Calibration ◽

Lake Qinghai ◽

Vicarious Calibration ◽

Calibration Methods ◽

Spectral Imager

To calibrate the low signal response of the ocean color (OC) bands and test the stability of the Fengyun-3D (FY-3D)/Medium Resolution Spectral Imager II (MERSI-II), an absolute radiometric calibration field test of FY-3D/MERSI-II at the Lake Qinghai Radiometric Calibration Site (RCS) was carried out in August 2018. The lake surface and atmospheric parameters were mainly measured by advanced observation instruments, and the MODerate spectral resolution atmospheric TRANsmittance algorithm and computer model (MODTRAN4.0) was used to simulate the multiple scattering radiance value at the altitude of the sensor. The results showed that the relative deviations between bands 9 and 12 are within 5.0%, while the relative deviations of bands 8, and 13 are 17.1%, and 12.0%, respectively. The precision of the calibration method was verified by calibrating the Aqua/Moderate-resolution Imaging Spectroradiometer (MODIS) and National Polar-orbiting Partnership (NPP)/Visible Infrared Imaging Radiometer (VIIRS), and the deviation of the calibration results was evaluated with the results of the Dunhuang RCS calibration and lunar calibration. The results showed that the relative deviations of NPP/VIIRS were within 7.0%, and the relative deviations of Aqua/MODIS were within 4.1% from 400 nm to 600 nm. The comparisons of three on-orbit calibration methods indicated that band 8 exhibited a large attenuation after launch and the calibration results had good consistency at the other bands except for band 13. The uncertainty value of the whole calibration system was approximately 6.3%, and the uncertainty brought by the field surface measurement reached 5.4%, which might be the main reason for the relatively large deviation of band 13. This study verifies the feasibility of the vicarious calibration method at the Lake Qinghai RCS and provides the basis and reference for the subsequent on-orbit calibration of FY-3D/MERSI-II.

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Towards Transabdominal Functional Photoacoustic Imaging of the Placenta: Improvement in Imaging Depth Through Optimization of Light Delivery

Annals of Biomedical Engineering ◽

10.1007/s10439-021-02777-0 ◽

2021 ◽

Author(s):

Kristie Huda ◽

Kenneth F. Swan ◽

Cecilia T. Gambala ◽

Gabriella C. Pridjian ◽

Carolyn L. Bayer

Keyword(s):

Delivery System ◽

Light Propagation ◽

Ex Vivo ◽

Photoacoustic Imaging ◽

Incidence Angle ◽

Incident Angle ◽

Placental Tissue ◽

Light Delivery ◽

Imaging Depth ◽

The Impact

AbstractFunctional photoacoustic imaging of the placenta could provide an innovative tool to diagnose preeclampsia, monitor fetal growth restriction, and determine the developmental impacts of gestational diabetes. However, transabdominal photoacoustic imaging is limited in imaging depth due to the tissue’s scattering and absorption of light. The aim of this paper was to investigate the impact of geometry and wavelength on transabdominal light delivery. Our methods included the development of a multilayer model of the abdominal tissue and simulation of the light propagation using Monte Carlo methods. A bifurcated light source with varying incident angle of light, distance between light beams, and beam area was simulated to analyze the effect of light delivery geometry on the fluence distribution at depth. The impact of wavelength and the effects of variable thicknesses of adipose tissue and muscle were also studied. Our results showed that the beam area plays a major role in improving the delivery of light to deep tissue, in comparison to light incidence angle or distance between the bifurcated fibers. Longer wavelengths, with incident fluence at the maximum permissible exposure limit, also increases fluence within deeper tissue. We validated our simulations using a commercially available light delivery system and ex vivo human placental tissue. Additionally, we compared our optimized light delivery to a commercially available light delivery system, and conclude that our optimized geometry could improve imaging depth more than 1.6×, bringing the imaging depth to within the needed range for transabdominal imaging of the human placenta.

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