Low Reflectance Targets Research Articles

Absolute radiometric calibration with lunar surface reflectance as reference for earth-observing VNIR camera

The absolute radiometric accuracy of earth-observing camera is crucial for the applications of natural resources, environment, agriculture and other industries. To continue the progress in this filed, a lunar surface reflectance based radiometric calibration approach is given in this paper. We chose IIM, M3, SP lunar models as references and GF-4 VNIR camera as sensor under calibrating. The lunar calibration sites were MS-2 site, Apollo-16 site and CE-3 site. The equivalent reflectance models of lunar were retrieved by Multiplying and integrating with the spectral response function of VNIR camera. Absolute radiometric calibrations with the equivalent reflectance models of lunar were carried out for 520–590nm, 630–690nm and 770–890nm spectral bands. The ground-based validation experiments were conducted with low, medium and high reflectance targets. The calibration accuracy was evaluated by comparing the relative errors of derived radiance after radiometric calibration with the benchmarks of TOA radiance transferred by in-situ measured reflectance. Lunar-based calibration models, lab and on-orbit filed-based models were used to compare the relative errors between proposed method and traditional way. The results showed that using IIM lunar model had better radiometric accuracy than other models, and SP model had the similar performance with traditional on-orbit filed-based model. The results indicated that using lunar to calibrate the earth-observing camera had the capability to improve the radiometric calibration accuracy.

Radiometric calibration of a large-array commodity CMOS multispectral camera for UAV-borne remote sensing

• An indoor and outdoor integrated radiometric calibration method for large-array commodity CMOS multispectral cameras. • A nonlinear quantum efficiency calibration model for poor linearity sensors. • A dark target-based empirical line method for low altitude atmospheric correction. • Compared with fitting methods, the lookup table method is a better vignetting effect correction method. To meet the requirement of high-resolution and high-efficiency unmanned aerial vehicle (UAV)-borne multispectral remote sensing, using the miniaturized large-array commodity complementary metal-oxide semiconductor (CMOS) camera is an effective solution. Given the characteristics of the new sensor and platform, almost no systematic and feasible radiometric calibration method has been specifically developed. In this paper, we proposed an indoor and outdoor integrated radiometric calibration method. To develop a systematic indoor calibration method, we explored the optimal methods for dark current offset, vignetting effect correction, and quantum efficiency calibration. According to the comparison results of three different methods, the lookup table (LUT) method was chosen to correct vignetting effect rather than nonlinear regression. Further, we proposed an exponential nonlinear model to replace the traditional linear model for quantum efficiency calibration, which improved the R-squares from around 0.92 to around 0.99. The outdoor calibration included atmospheric path radiance and reflectance correction. We proposed an empirical line method based on the dark target method to correct the atmospheric path radiance before the reflectance correction. Based on our method, the mean absolute percentage errors (MAPE) between the observed reflectance and the true reflectance were around 10%. Moreover, the method can greatly improve the calculated reflectance accuracy of low reflectance targets. Our method can serve as a useful reference for the radiometric calibration of large-array commodity CMOS multispectral cameras. It can also contribute to the application of UAV-borne multispectral remote sensing.

Potential of active multispectral lidar for detecting low reflectance targets.

The calibration and sampling of the multispectral Light Detection and Ranging (lidar) intensity is still challenging because the data acquisition has to be optimized for simultaneous 3D measurement, and the intensity retrieval methods need to be fast to enable real-time detection. We have studied the spectral measurement of low reflectance targets with an 8-channel hyperspectral lidar with improved waveform sampling and sensitivity, which now allow the detection of spectral differences even at low reflectance values. Our initial analysis resulted in a classification accuracy greater than 80%, which indicates that the multispectral lidar is able to detect the small differences in target spectral properties when reflectance at two or more channels is compared at the same time.

水下二维及三维距离选通成像去噪技术研究

Compared with traditional underwater cameras, the detection distance of underwater range-gated imaging can be increased by 2-3 times. Furthermore, based on this technology, fast high-resolution 3D imaging can be achieved. It has great potentials in underwater target detection and recognition, automatic navigation, marine scientific research and natural resources exploration. Although range-gated imaging can suppress the backscattering noise by space slicing, and achieve higher quality images, the backscattering noise of the sampling water volume still exists in gated images, resulting in low image signal-to-noise ratio and contrast, especially for distant targets or low reflectance targets. This paper systematically introduced author's research of deblurring methods for 2D and 3D range-gated imaging. In 2D imaging, two methods were proposed:the first was an algorithm of self-adaptive double-plateau histogram equalization to improve image contrast and better meet human vision; the second was to use a water-noise-reference denoising algorithm to improve the signal-to-noise ratio of target gated images. In 3D imaging, there were also two methods proposed:one was to use the water-noise-reference denoising algorithm for 3D reconstruction, and the other was to use the threshold-dependent joint bilateral filter algorithm for enhancing 3D images. The four proposed methods can be used independently or in combination for denoising enhancement of underwater range gated imaging.

Drivers’ detection of roadside targets when driving vehicles with three headlight systems during high beam activation

A previous open-road experiment indicated that curve-adaptive HID headlights driven with low beams improved drivers’ detection of low conspicuity targets compared with fixed halogen and fixed HID low beam systems. The current study used the same test environment and targets to assess whether drivers’ detection of targets was affected by the same three headlight systems when using high beams. Twenty drivers search and responded for 60 8×12inch targets of high or low reflectance that were distributed evenly across straight and curved road sections as they drove at 30 mph on an unlit two-lane rural road. The results indicate that target detection performance was generally similar across the three systems. However, one interaction indicated that drivers saw low reflectance targets on straight road sections from further away when driving with the fixed halogen high beam condition compared with curve-adaptive HID high beam headlights and also indicated a possible benefit for the curve-adaptive HID high beams for high reflectance targets placed on the inside of curves. The results of this study conflict with the previous study of low beams, which showed a consistent benefit for the curve-adaptive HID low beams for targets placed on curves compared with fixed HID and fixed halogen low beam conditions. However, a comparison of mean detection distances from the two studies indicated uniformly longer mean target detection distances for participants driving with high beams and implicates the potential visibility benefits for systems that optimize proper high beam use.

Shadow detection improvement using spectral indices and morphological operators in high resolution images from urban areas

Abstract. While high-resolution remote sensing images have increased application possibilities for urban studies, the large number of shadow areas has created challenges to processing and extracting information from these images. Furthermore, shadows can reduce or omit information from the surface as well as degrading the visual quality of images. The pixels of shadows tend to have lower radiance response within the spectrum and are often confused with low reflectance targets. In this work, a shadow detection method was proposed using a morphological operator for dark pattern identification combined with spectral indices. The aims are to avoid misclassification in shadow identification through properties provided by them on color models and, therefore, to improve shadow detection accuracy. Experimental results were tested applying the panchromatic and multispectral band of WorldView-2 image from São Paulo city in Brazil, which is a complex urban environment composed by high objects like tall buildings causing large shadow areas. Black top-hat with area injunction was applied in PAN image and shadow identification performance has improved with index as Normalized Difference Vegetation Index (NDVI) and Normalized Saturation-Value Difference Index (NSDVI) ratio from HSV color space obtained from pansharpened multispectral WV-2 image. An increase in distinction between shadows and others objects was observed, which was tested for the completeness, correctness and quality measures computed, using a created manual shadow mask as reference. Therefore, this method can contribute to overcoming difficulties faced by other techniques that need shadow detection as a first necessary preprocessing step, like object recognition, image matching, 3D reconstruction, etc.

Objective Evaluation Method for Appearance of Fabric Wrinkling by the CCD Laser Light Measuring System

The method evaluating the wrinkle appearance objectively with the CCD laser displacement sensor (CCD-LDS) system was described in the paper. A CCD was employed as the light-receiving element in the system, whose sensor enables to obtain the stably, highly accurate displacement measurement, regardless of the light quantity distribution of the beam spot. The wrinkle grades of standard replicas and fabrics were measured and analyzed with the system, which was an excellent tool for investigating 3-D surface shapes of wrinkles. The contours of wrinkle surfaces were also analyzed with the fractal method. Following conclusions were obtained: 1) it provided the high precision for measuring wrinkle shapes; 2) Fractal dimensions of wrinkle surfaces could quantify the wrinkle grades of replicas; 3) the system enabled to measure the multicolored, patterned, or low reflective targets.

Assessment of different spectral indices in the red-near-infrared spectral domain for burned land discrimination

A new spectral index named Burned Area Index (BAI), specifically designed for burned land discrimination in the red-near-infrared spectral domain, was tested on multitemporal sets of Landsat Thematic Mapper (TM) and NOAA Advanced Very High Resolution Radiometer (AVHRR) images. The utility of BAI for burned land discrimination was assessed against other widely used spectral vegetation indices: Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI) and Global Environmental Monitoring Index (GEMI). BAI provided the highest discrimination ability among the indices tested. It also showed a high variability within scorched areas, which reduced the average normalized distances with respect to other indices. A source of potential confusion between burned land areas and low-reflectance targets, such as water bodies and cloud shadows, was identified. Since BAI was designed to emphasize the charcoal signal in post-fire images, this index was highly dependent on the temporal permanence of charcoal after fires.

Simulation of spectral planetary reflectance of targets

Um modelo físico é estabelecido para simular a reflectância planetária de diferentes alvos de uma região do nordeste do Brasil. O modelo simula o sinal detectado por um sensor como uma função de sucessivas ordens de interação da radiação solar com o sistema terra-atmosfera. Uma precisa expressão analítica é estabelecida para determinar a reflectância aparente de uma superfície uniforme isotrópica, incluindo-se os efeitos de absorção de gases e espalhamento molecular e de aerossóis. A atmosfera é considerada como uma mistura de ar e aerossóis. O método "single scattering" é utilizado para determinar a reflectância intrínseca da atmosfera. A parametrização dupla de Henyey-Greenstein é utilizada para representar a função de fase dos aerossóis. Os parâmetros ópticos atmosféricos são obtidos da literatura, exceto a profundidade óptica dos aerossóis que foi avaliada através de dados piranométricos. O modelo é aplicado para simular a reflectância planetária no intervalo espectral de 0,4 a 1,1 <FONT FACE="Symbol">m</font>m e também para simular o sinal detectado nas bandas 1, 2, 3 e 4 do sensor TM do satélite Landsat-5, de áreas caracterizadas espectralmente (água, solo e vegetação). Os resultados mostram que a reflectância da atmosfera é predominante na reflectância planetária para alvos de baixa reflectância, mesmo quando a profundidade óptica dos aerossóis é pequena. No caso de alvos com média reflectância (solo e vegetação), a contribuição da atmosfera é pouco notada, pois a reflectância planetária é predominantemente representada pela reflectância do alvo.

Calibration of GMS-VISSR, features of MOS-VTIR and Landsat MSS

The analyses of sensitivity of visible channel of Visible and Infrared Spin Scan Radiometer onboard Geostationary Meteorological Satellite(GMS)-3 and -4 indicate stable for low reflective targets while a significant decreasing tendency with time for high reflective targets. Equations to correct the effect of temporal degradation are derived. Verification of data acquired with Visible and Thermal Infrared Radiometer onboard Marine Observation Satellite indicates that the Calibration is reasonable. Comparison of Landsat MSS image data processed at NASDA and NASA indicates a slight difference. It is found that the gain of Landsat-2 and -3 MSS is influenced by brightness of targets.