Patent ID: 12248076

DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiments of the present invention will be described hereinbelow in conjunction with the above-described drawings.FIG.1shows a perspective view illustrating the general operation of the imaging lens20, imaging lens plane30, image plane50and object plane40in the Scheimpflug condition when both the object plane40and image plane50are tilted with respect to the imaging lens plane30, as applicable to the present invention. As illustrated, if considered in three dimensions, the three planes represented inFIG.1would extend out of the page. In the Scheimpflug condition, the image plane50is in focus along the object plane40. The object plane portion from A to B inFIG.1correspond to locations A′ and B′ in the image plane50. The lens plane30, object plane40and image plane50intersect at a common line60that extends out of the page.

FIG.2shows how the Scheimpflug condition illustrated inFIG.1is implemented with the imaging lens20and a laser beam250in what is often called a Scheimpflug LIDAR or a Scheimpflug Correlation LIDAR. In a Scheimpflug LIDAR200, the laser beam250lies in the object plane40and a linear detector array230lies in the image plane50between points A′ and B′ (referring back toFIG.1). The linear detector array230may be implemented using any device known in the art, such as a CCD or an imaging detector, that includes a plurality of detector elements or equivalent. For example, the linear detector array may be implemented using a detector device having an array of detector elements that can be electronically controlled to be divided into a plurality of sub-arrays; each sub-array would constitute a single detector element.

Each element in the detector array230is configured to view a different portion of the laser beam250as illustrated by the hash marks270along the laser beam250inFIG.2. The letters A and B indicate the extent of the field of view280of the linear array230in the object plane. A optical bandpass filter225is positioned in front of the imaging lens20and the detector array230. The bandpass filter is intended to reduce the background illumination and improves the signal to noise ratio.

Instead of using time of flight to determine the location along the laser beam or object plane40, the Scheimpflug condition defines the distance along the laser beam250. Therefore, the detector230does not require the large bandwidth of a time of flight system to resolve range. The Scheimpflug LIDAR may use a CW laser and because it does not use Doppler to determine speed, the laser does not need to meet the challenging coherence requirements of a Doppler based system.

FIG.3shows a preferred embodiment according to the present invention, wherein two laser beams250and251are used in implementing the Scheimpflug LIDAR system for observing a region of higher aerosol concentration260moving in the direction indicated by the arrow265. The preferred embodiment of the present invention requires at least two laser beams250, and251pointed in different directions and the separation between beams increases with distance from the LIDAR200as shown inFIG.3, along with corresponding linear detector arrays230and231positioned to view the scattered light from corresponding laser beams250and251, respectively. While two lasers270and271are shown in the preferred embodiment, an alternative embodiment could be configured to use a single laser and split the beam into two beams using a beam splitter. The linear detector arrays230and231produce output signals290and291, respectively, that are directed to the digitizer/frame buffer300.

The digitizer/frame buffer300may be implemented only as a frame buffer depending upon the type of linear detector array selected. Some linear array detectors will have the digitization function integrated into the linear detector array; if that type of device is used, the digitizer/frame buffer300will only provide a frame buffer function. The frame buffer output goes to the processor310where the signals for each detector element in the linear detector arrays230and231will be converted to time series data that can be graphically represented in an intensity versus time format. These time series data will then be cross correlated as described below for the detector pairs that are selected for processing. The cross correlation will be output to the data archive and user interface320. For example, given a concentration of aerosols260(say a puff of smoke) that is moving in the direction of the large arrow265, as the concentration of aerosols increases, the aerosol scattering will increase resulting in an increase in the aerosol scattering signal level.

FIGS.4A and4Bshow plots of a simulated signal from two laser beams for a given range in the case where the wind is in the plane of the beams. In particular,FIGS.4A and4Bshow a pair of plots representing the signals from the LIDAR200resulting from the two laser beams250and251and selected detector elements from the linear detector arrays230and231that correspond to a given range. In other words, the detector elements selected from the linear detector arrays230and231are the ones that are positioned to view the corresponding positions or ranges of their respective laser beams250and251. The plot ofFIG.4Ashows the increased signal level251SIGNAL resulting from the increased concentration of aerosols encountering laser beam251. As time progresses, the signal level increases and then decreases. The plot ofFIG.4Bshows signal250SIGNAL from the aerosols interacting with the second laser beam250. Note that the two signal levels are not exactly alike as atmospheric turbulence will cause the aerosol concentration to change with time and location.

Cross correlation calculations based on the formulas hereinbelow between the two signals with a known sample rate gives the amount of time it takes for the aerosol concentration to pass by both beams. The letter h is the height or range from the LIDAR to the area viewed by the LIDAR. Time is identified as the letter t and the wind velocity is represented by the letter V.

time⁢⁢delay@h=max⁡[S⁢i⁢g1⁡(r,t)*S⁢i⁢g2⁡(r,t)]⌉rh⁢⁢∂∂τ⁡[∫-∞∞⁢S⁢i⁢g1⁡(r,t)*S⁢i⁢g2⁡(r,t+τ)⁢dt]τh=0Vw⁢i⁢n⁢dh=beam⁢⁢separation@htime⁢⁢delay@h
Since the geometry or range is known from the design, the speed is obtained by dividing the distance between the two laser beams by the correlation time. As shown inFIG.4B, the section TD on the plot represents the time difference or time delay that then is used to determine the speed.

In the above discussion, the cross correlation was calculated between two detectors corresponding to a given range, but cross correlations may be calculated between signals from any pair of the detector elements in the linear detector arrays230and231.FIG.3, as an example, shows the aerosol moving nearly perpendicular to the laser beam. Thus, it is possible to measure movement along the laser beam by using pairs of detectors along a laser's propagation direction.

While only two laser beams are shown in the above discussion of the preferred embodiment, additional laser beams may be used to refine the measurement of wind speed and direction. For example, a third laser beam directed out of the plane defined by any two lasers would provide information that would allow one to measure the three dimensional wind vector.

Cross correlation between two or more signals can also be analyzed using machine learning methods. By training the system with truth data, machine learning algorithm can predict and/or supplement the measurement of wind speed and direction.

Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.