Passive infrared gas imaging systems have been utilized in the equipment leak detection and repair in chemical
manufacturers and petroleum refineries. The detection performance mainly relates to the sensitivity of infrared detector,
optical depth of gas, atmospheric transmission, wind speed, and so on. Based on our knowledge, the spatial concentration
distribution of continuously leaking gas plays an important part in leak detection. Several computational model of gas
diffusion were proposed by researchers, such as Gaussian model, BM model, Sutton model and FEM3 model. But these
models focus on calculating a large scale gas concentration distribution for a great amount of gas leaks above over 100-
meter height, and not applicable to assess detection limit of a gas imaging system in short range. In this paper, a wind
tunnel experiment is designed. Under different leaking rate and wind speed, concentration in different spatial positions is
measured by portable gas detectors. Through analyzing the experimental data, the two parameters σy(x) and σz (x) that
determine the plume dispersion in Gaussian model are adjusted to produce the best curve fit to the gas concentration
data. Then a concentration distribution model for small mount gas leakage in short range is established. Various gases,
ethylene and methane are used to testify this model.
The fingerprint region of most gases is within 3 to 14μm. A mid-wave or long-wave infrared thermal imager is therefore
commonly applied in gas detection. With further influence of low gas concentration and heterogeneity of infrared focal
plane arrays, the image has numerous drawbacks. These include loud noise, weak gas signal, gridding, and dead points,
all of which are particularly evident in sequential images. In order to solve these problems, we take into account the
characteristics of the leaking gas image and propose an enhancement method based on adaptive time-domain filtering
with morphology. The adaptive time-domain filtering which operates on time sequence images is a hybrid method
combining the recursive filtering and mean filtering. It segments gas and background according to a selected threshold;
removes speckle noise according to the median; and removes background domain using weighted difference image. The
morphology method can not only dilate the gas region along the direction of gas diffusion to greatly enhance the
visibility of the leakage area, but also effectively remove the noise, and smooth the contour. Finally, the false color is
added to the gas domain. Results show that the gas infrared region is effectively enhanced.
Leakage of dangerous gases will not only pollute the environment, but also seriously threat public safety. Thermal infrared
imaging has been proved to be an efficient method to qualitatively detect the gas leakage. But some problems are remained,
especially when monitoring the leakage in a passive way. For example, the signal is weak and the edge of gas cloud in the
infrared image is not obvious enough. However, we notice some important characteristics of the gas plume and therefore
propose a gas cloud infrared image enhancement method based on anisotropic diffusion. As the gas plume presents a large
gas cloud in the image and the gray value is even inside the cloud, strong forward diffusion will be used to reduce the noise
and to expand the range of the gas cloud. Frames subtraction and K-means cluttering pop out the gas cloud area.
Forward-and-Backward diffusion is to protect background details. Additionally, the best iteration times and the time step
parameters are researched. Results show that the gas cloud can be marked correctly and enhanced by black or false color,
and so potentially increase the possibility of gas leakage detection.
Standoff detection of gas leakage is a fundamental need in petrochemical and power industries. The passive gas imaging
system using thermal imager has been proven to be efficient to visualize leaking gas which is not visible to the naked
eye. The detection probability of gas leakage is the basis for designing a gas imaging system. Supposing the performance
parameters of the thermal imager are known, the detectivity based on electromagnetic radiation transfer model to image
gas leakage is analyzed. This model takes into consideration a physical analysis of the gas plume spread in the
atmosphere-the interaction processes between the gas and its surrounding environment, the temperature of the gas and
the background, the background surface emissivity, and also gas concentration, etc. Under a certain environmental
conditions, through calculating the radiation reaching to the detector from the camera's optical field of view, we obtain
an entity "Gas Equivalent Blackbody Temperature Difference (GEBTD)" which is the radiation difference between the
on-plume and off-plume regions. Comparing the GEBTD with the Noise Equivalent Temperature Difference (NETD) of
the thermal imager, we can know whether the system can image the gas leakage. At last, an example of detecting CO2 gas by JADE MWIR thermal imager with a narrow band-pass filter is presented.
KEYWORDS: Data storage, Geographic information systems, Internet, Data modeling, Data communications, Web services, Databases, Navigation systems, Zoom lenses, Data transmission
WebGIS is the technology which publishes the geographic information service through the internet; it is changing more
perfect after years with rich information, perfect user experience, which offer convenient geographic information
services to people. This paper analyzes the technology and the schema used in the WebGIS today, and puts forward a
schema which is based on oracle spatial, Ajax, JavaScript and so on. First, it uses oracle 10g to store the spatial data in
the service, which provide GEOLOC field to store the spatial information and some spatial query and analysis functions
and operators which make it easy and fast to realize spatial computation. Second it uses Ajax schema which realize
asynchronous operations between client and service, and let the user do not need to wait before the service return the
result. Third it uses the tile method that the large map is sliced up into many tiles and stored in the server. When the user
visits the site, it just needs to download the several small tiles to visualize. Last, in the client, many operations such as
pan, zoom and so on are realized based on the pure JavaScript. This schema solves the big data transmission through the
internet, which reduce the response time when people visit the site and improve the users' experience.
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