Journal Paper - 2018 by CHIMAN KWAN
Remote Sensing, 2018
We present a simple, and efficient approach to fusing MODIS and Landsat images. It is well known ... more We present a simple, and efficient approach to fusing MODIS and Landsat images. It is well known that MODIS images have high temporal resolution and low spatial resolution, whereas Landsat images are just the opposite. Similar to earlier approaches, our goal is to fuse MODIS and Landsat images to yield high spatial and high temporal resolution images. Our approach consists of two steps. First, a mapping is established between two MODIS images, where one is at an earlier time, t 1 , and the other one is at the time of prediction, t p. Second, this mapping is applied to map a known Landsat image at t 1 to generate a predicted Landsat image at t p. Similar to the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM), SpatioTemporal Image-Fusion Model (STI-FM), and the Flexible Spatiotemporal DAta Fusion (FSDAF) approaches, only one pair of MODIS and Landsat images is needed for prediction. Using seven performance metrics, experiments involving actual Landsat and MODIS images demonstrated that the proposed approach achieves comparable or better fusion performance than that of STARFM, STI-FM, and FSDAF.
Remote Sensing, 2018
High resolution (HR) hyperspectral (HS) images have found widespread applications in terrestrial ... more High resolution (HR) hyperspectral (HS) images have found widespread applications in terrestrial remote sensing applications, including vegetation monitoring, military surveillance and reconnaissance, fire damage assessment, and many others. They also find applications in planetary missions such as Mars surface characterization. However, resolutions of most HS imagers are limited to tens of meters. Existing resolution enhancement techniques either require additional multispectral (MS) band images or use a panchromatic (pan) band image. The former poses hardware challenges, whereas the latter may have limited performance. In this paper, we present a new resolution enhancement algorithm for HS images that only requires an HR color image and a low resolution (LR) HS image cube. Our approach integrates two newly developed techniques: (1) A hybrid color mapping (HCM) algorithm, and (2) A Plug-and-Play algorithm for single image super-resolution. Comprehensive experiments (objective (five performance metrics), subjective (synthesized fused images in multiple spectral ranges), and pixel clustering) using real HS images and comparative studies with 20 representative algorithms in the literature were conducted to validate and evaluate the proposed method. Results demonstrated that the new algorithm is very promising.
Sensors, 2018
Although Worldview-2 (WV) images (non-pansharpened) have 2-m resolution, the re-visit times for t... more Although Worldview-2 (WV) images (non-pansharpened) have 2-m resolution, the re-visit times for the same areas may be seven days or more. In contrast, Planet images are collected using small satellites that can cover the whole Earth almost daily. However, the resolution of Planet images is 3.125 m. It would be ideal to fuse these two satellites images to generate high spatial resolution (2 m) and high temporal resolution (1 or 2 days) images for applications such as damage assessment, border monitoring, etc. that require quick decisions. In this paper, we evaluate three approaches to fusing Worldview (WV) and Planet images. These approaches are known as Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM), Flexible Spatiotemporal Data Fusion (FSDAF), and Hybrid Color Mapping (HCM), which have been applied to the fusion of MODIS and Landsat images in recent years. Experimental results using actual Planet and Worldview images demonstrated that the three aforementioned approaches have comparable performance and can all generate high quality prediction images.
IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, 2018
Anomaly detection has been known to be a challenging problem due to the uncertainty of anomaly an... more Anomaly detection has been known to be a challenging problem due to the uncertainty of anomaly and the interference of noise. In this paper, we focus on anomaly detection in hyperspectral images (HSI) and propose a novel detection algorithm based on spectral unmixing and dictionary based low-rank decomposition. The innovation is threefold. First, due to the highly mixed nature of pixels in HSI data, instead of using the raw pixel directly for anomaly detection, the proposed algorithm applies spectral unmixing to obtain the abundance vectors and uses these vectors for anomaly detection. We show that the abundance vectors possess more distinctive features to identify anomaly from background. Second, to better represent the highly-correlated background and the sparse anomaly, we construct a dictionary based on the mean-shift clustering of the abundance vectors to improve both the discriminative and representative power of the algorithm. Finally, a low-rank matrix decomposition method based on the constructed dictionary is proposed to encourage the coefficients of the dictionary, instead of the background itself, to be low-rank, and the residual matrix to be sparse. Anomalies can then be extracted by summing up the columns of the residual matrix. The proposed algorithm is evaluated on both synthetic and real datasets. Experimental results show that the proposed approach constantly achieves high detection rate, while maintaining low false alarm rate regardless of the type of images tested.
Sensors, 2018
Hyperspectral images with hundreds of spectral bands have been proven to yield high performance i... more Hyperspectral images with hundreds of spectral bands have been proven to yield high performance in material classification. However, despite intensive advancement in hardware, the spatial resolution is still somewhat low, as compared to that of color and multispectral (MS) imagers. In this paper, we aim at presenting some ideas that may further enhance the performance of some remote sensing applications such as border monitoring and Mars exploration using hyperspectral images. One popular approach to enhancing the spatial resolution of hyperspectral images is pansharpening. We present a brief review of recent image resolution enhancement algorithms, including single super-resolution and multi-image fusion algorithms, for hyperspectral images. Advantages and limitations of the enhancement algorithms are highlighted. Some limitations in the pansharpening process include the availability of high resolution (HR) panchromatic (pan) and/or MS images, the registration of images from multiple sources, the availability of point spread function (PSF), and reliable and consistent image quality assessment. We suggest some proactive ideas to alleviate the above issues in practice. In the event where hyperspectral images are not available, we suggest the use of band synthesis techniques to generate HR hyperspectral images from low resolution (LR) MS images. Several recent interesting applications in border monitoring and Mars exploration using hyperspectral images are presented. Finally, some future directions in this research area are highlighted.
IEEE Trans. on Aerospace and Electronic Systems, 2018
The use of unmanned aerial vehicles (UAV) in military and industry today is becoming more widespr... more The use of unmanned aerial vehicles (UAV) in military and industry today is becoming more widespread. There are a wide range of UAV models that are functional today. The size of these UAVs can be as small as a hawk and can be as big as a passenger jetliner. It is critical for these UAVs to have contingency plans before flight in case of unexpected situations, such as engine-out events which cause total loss of thrust during flight. An important part of contingency planning is to identify emergency landing sites along the flight path of the UAV. This paper discusses the development of an offline semi-automated approach for finding emergency landing sites in the shape of a rectangular runway to be used in preflight contingency planning. The approach introduces a total of five emergency landing measures and a surface type estimation which are applied to the identified emergency landing site candidates for their safety assessment. The output is a list of emergency landing site candidates together with their surface type estimates that are ranked from the safest to least safe through a generalized safety score for each surface type. The approach can label the ranked landing site candidates according to their reachability in the presence of wind given the UAV's altitude and coordinates at the time the total loss of thrust happened and the wind forecast for the area.
AIAA Journal of Guidance, Control and Dynamics, 2018
This Note’s key contribution is to provide a numerical solution for
a time-constrained bang–bang–... more This Note’s key contribution is to provide a numerical solution for
a time-constrained bang–bang–bang (BBB)-type extremal trajectory
design in the existence of steady wind conditions for a fixed-wing
UAVnavigating from one point to a nearby point.
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Journal Paper - 2018 by CHIMAN KWAN
a time-constrained bang–bang–bang (BBB)-type extremal trajectory
design in the existence of steady wind conditions for a fixed-wing
UAVnavigating from one point to a nearby point.