Patent Application
20100014066
Starting at sea level, the troposphere goes up seven miles. The bottom one third, that which is closest to us, contains 50% of all atmospheric gases. This bottom one third is the only part of the whole makeup of the atmosphere that is breathable. This is the only area where all weather takes place. Troposphere means, literally, “where the air turns over”. This is a very appropriate name, since within the troposphere, the air is in a constant up and down flow.
Also in this layer, the air is hotter closer to the earth's surface and colder air is higher up. As the hotter air rises admitting the colder air to the area near the ground, additional and complex air flows are generated. As air flows over objects close to the ground, it will roil, just like water flowing over a rock. This roiling air is known as turbulence. Turbulence is very dangerous to skydivers because if a jumper gets caught in a downward flow of air, it will accelerate the parachutist toward the ground, which can result in injury or death. Up drafts, down drafts, and winds from side to side all act to displace a skydiver or an inanimate package dropped by parachute from the intended landing zone.
Unlike water on a river, this flow is invisible, so skydivers must be aware of the objects that cause turbulence such as buildings, trees, or mountains. Depending on wind speed, turbulence can be created downwind of that obstacle at a distance of ten to twenty times the height of the obstacle.
The differential between time under the canopy and time in freefall can also make the prediction of a landing site even more difficult. A 10 mile per hour wind, for example, will drift a skydiver a half mile in a normal 3,000 foot descent under canopy. Because a skydiver in freefall is falling at speeds ranging from 120 mph and 180 mph on average, a skydiver will remain in freefall for between 45 seconds to a minute, and while displaced by winds, both of exposure time and sail area are very different than when falling under canopy.
Presently, the preferred method for measuring winds aloft is observation of the release and ascent of a balloon, requiring helium tanks, stopwatches, and a crude inclination measurement device. At that, the results are generally less exact than would be desired. Additionally, where the parachute drop is a military drop, and the landing site is in a territory that is under fire, release of a balloon gives notice to an enemy that a drop is imminent.
In many instances, contact with a ground party is not possible or at least, not desirable. In relief operations after natural disasters, rapid, accurate drops of supplies cannot be reliably coordinated given the compromised infrastructure that may then exist.
What is needed is a method and apparatus for estimating from an aircraft the invisible movement of air in proximity to a landing zone.
A Doppler LIDAR works on the principle that light scattered from a moving object is frequency shifted with respect to the incident light. If a collimated beam of light of wavelength X is incident on a moving surface, the frequency or Doppler shift of the light scattered from the surface is calculable. Laser Doppler velocimetry (“LDV”) is a technique for measuring the direction and speed of fluids like air and water and is somewhat akin to using an interferometer. A beam of monochromatic laser light is sent into the flow, and particles, or motes, within the flow will reflect light with a Doppler shift corresponding to their velocities. The shift can be measured by interfering the reflected beam with the original beam, which will form a beat frequency difference proportional to the velocity.
The LDV can assess the velocity of wind by ascertaining the velocity vector of motes within the flow of wind. LDV systems provide wind speed data by measuring the Doppler shift imparted to laser light that is scattered from natural aerosols (e.g. dust, pollen, water droplets etc.) present in air. LDV systems measure the Doppler shift imparted to reflected radiation within a certain remote probe volume and can thus only acquire wind velocity data in a direction parallel to the transmitted laser beam. In the case of a LDV device located on the ground, it is possible to measure the true (3D) wind velocity vector a given distance above the ground by scanning the LDV in a controlled manner; for example using a conical scan. This enables the wind vector to be intersected at a range of known angles thereby allowing the true wind velocity vector to be constructed.
An airborne wind profiler air drops includes a system bus for receiving a GPS signal including a time and position solution and an attitude signal representing heading and inclination of the wind profiler. An optical module includes at least one laser Doppler velocimeter including an mount allowing the at least one laser Doppler velocimeter to articulate in at least two axes, thereby to provide sufficiently unique velocity data to construct a true wind velocity vector. The velocimeter signal includes at least one first radial velocity of a first wind-borne aerosol and a first orientation of the at least one laser Doppler velocimeter relative to the orientation of the device. A processor module receives the first velocimeter signal at the time from at least one laser Doppler velocimeter.
In accordance with further aspects of the invention, a platform for a handheld wind profiler includes a housing containing a three-axis magnetic compass module generating a compass signal including the orientation of the housing relative to magnetic north at a time. A two-axis inclinometer module generates an inclinometer signal including the orientation of the housing relative to a horizontal plane at the time. A GPS module generating a GPS signal indicating a time and position solution including a terrain position of the housing based upon the time. A processor receives a first velocimeter signal at the time from at least one laser Doppler velocimeter. The velocimeter signal includes a first radial velocity of a first wind-borne aerosol and a first orientation of the at least one laser Doppler velocimeter relative to the housing. The processor resolves the first velocimeter signal to determine an orientation of the at least one laser Doppler velocimeter relative to magnetic north.
The present invention comprises a system for orienting the hand held wind profiler with respect to magnetic north. The GPS position solution is used to calculate the deviation of the three-axis magnetic compass indication of north relative to geographic north. This enables the wind profiler to report wind direction and velocity relative to true north regardless of the orientation of the wind profiler. The three-axis magnetic compass provides rotation independent indication of the direction of magnetic north while an inclinometer is used to orient the LDV with respect to a level plane.
Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:
a is a drawing of the exterior of a preferred embodiment;
b is a drawing of a cut away view of a preferred embodiment, and
A handheld, portable wind profiler for winds aloft includes a system bus for receiving a GPS signal including a time and position solution and a three-axis magnetic compass for determining magnetic north relative to the orientation of the winds aloft profiler and an 2-axis inclinometer to provide a level reference plane regardless of inclination of the device. An optical module includes at least one laser Doppler velocimeter including an mount allowing the at least one laser Doppler velocimeter to articulate in at least two axes, thereby to orient the laser Doppler velocimeter above the horizon to generate at least one first velocimeter signal. The velocimeter signal includes at least one first radial velocity of a first wind-borne aerosol and a first orientation of the at least one laser Doppler velocimeter relative to the ground. A processor module receives the first velocimeter signal at the time from at least one laser Doppler velocimeter.
As illustrated in
A GPS module 5 provides GPS time and position solutions. The GPS module 5 may include an integrated antenna or may have an external antenna attached. For non-limiting illustrative purposes, the GPS module 5 is shown as complete with an integrated antenna. A 3-axis compass 7 orients the platform relative to magnetic north. A two-axis inclinometer 9 is included to determine orientation of the platform relative to the horizon. A barometric pressure sensor 11 is used for both of determining altitude and local meteorological data. Temperature sensor 25 is used to determine ambient temperature and the combination of barometric pressure and temperature is used to calculate density altitude. Density altitude is essential to calculating the descent rate for parachute drops of cargo and personnel. Based upon the orientation of the LDV profiler 3 relative to the terrain, the at least one laser optics module 13 scanning of a terrain volume can reliably occur.
Power is provided by a battery and power supply module (“power module”) 4 through a power bus 21 to all active components, including those listed above and others to be introduced below.
A user interface includes a keyboard 19 and a graphic display 17. While a keyboard is portrayed in [Need correct
In normal operation, after the processor module 15 boots up, performs its power on self test (“POST”), and it begins processing by in turn initializing each of the GPS module 5, 3-axis compass 7, the inclinometer 9, the barometric sensor 11, temperature sensor 25, and the laser optics module 13 as well as the display module 17 and the keyboard 19 on the data bus 23. The GPS module 5 begins to receive ephemeris from those satellites “visible” to the profiler 3. Once the GPS has received at least four distinct ephemeredes, it solves for position and time. Once an at least two dimensioned position solution is derived, the processor module 15 is able to retrieve from a look up table resident in the processor module 15, a magnetic deviation corresponding to the position solution. At any point on the Earth there exists an angle between the local magnetic field—the direction the north end of a compass points—and true north, and that angle is known though varying very slowly and predictably over time. The magnetic deviation in a given area will change slowly over time, possibly as much as 2-25 degrees every hundred years or so, depending upon how far from the magnetic poles it is. The deviation is positive when the magnetic north is east of true north.
A 3-axis compass is essential for this application in that the magnetic field of the earth consists of a vector with a component directed parallel to the earth and a component directed into the earth. The relative magnitude of these two components varies with location on the surface of the earth. Because of the variation in the vector direction of the earth's magnetic field, a two-axis magnetic compass will exhibit direction errors that are dependent on the inclination of the compass from horizontal. At the equator, the magnetic field of the earth is essentially parallel to the surface of the earth and tilting a two-axis compass when near the equator will have no effect on the indication of magnetic north. Near the north or south magnetic poles, the field is directed nearly straight down into the earth and tilting a compass here will cause the compass to point more toward the surface of the earth and report erroneously on the direction of magnetic north. A three-axis compass measures the earth's magnetic field in three axes and measures the full magnetic field vector of the earth and can thereby correct for inclination of the compass and will always point correctly to magnetic north.
Magnetic deviation varies both from place to place, and with the passage of time. As a traveler cruises the east coast of the United States, for example, the declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10 degrees east (in Texas), meaning a compass adjusted at the beginning of the journey would have a true north error of over 30 degrees if not adjusted for the changing declination.
In most areas, the spatial variation reflects the irregularities of the flows deep in the earth; in some areas, deposits of iron ore or magnetite in the earth's crust may contribute strongly to the declination. Similarly, secular changes to these flows result in slow changes to the field strength and direction at the same point on the Earth. Nonetheless, the magnetic deviation in any one location may readily be determined based upon a location and time solution such as that provided by the GPS module 5. The processor module 15 readily retrieves a solution from a look-up table stored in the memory included in the processor module 15 based upon the GPS module 5 and the supplied position and time solution. Correction for magnetic deviation allows the compass module to correct for true north.
The inclinometer 9 registers inclination relative to two orthogonal axes which is sufficient for determining angular deviation with respect to a horizontal plane. This is necessary to correctly calculate the altitude of the Doppler shift indicated winds aloft, as inclination from horizontal will cause the result in a wind measurement altitude that is lower than the true altitude of the measurement and also slower, as the vector component along the direction of measurement decreases and the inclination angle increases. With such a determination, along with an indication from the three-dimensional compass as to the location of magnetic north, corrections can be effected that render a very good orientation of the hand-held profiler in real time relative to a three-dimensioned space within landing zone. Common sensor technologies for inclinometers are accelerometer, Liquid Capacitive, electrolytic, gas bubble in liquid, and pendulum. Any of the common two-axis technologies will serve to orient the handheld profiler 3.
Once, a position, an orientation in space relative to the horizon and relative to true north is known, the profiler 3, can, by virtue of the processor module 15, observe and describe the wind vectors in the projected thee-dimensioned space relative to cardinal points of a compass. In one embodiment of the profiler 3, three laser optics modules 13 are present in the profiler 3. The profiler 3 can perform its duties with as few as one laser optics module 13 and more than three laser optics modules 13 can provide more data for simultaneous measurement of wind velocity oriented advantageously in distinct directions in order to get still greater redundancy of data. One non-limiting embodiment of the profiler 3, however, advantageously exploits three laser optics modules 13 which are suitably orientable in the three-dimensioned space that the processor module 15 defines relative to the profiler 3. In such a configuration, the three laser optics modules 13 will readily allow a thorough and rapid scan of the three-dimensioned space.
Because the laser optics modules 13 measure the radial component of the air velocity (positive toward the laser optics module 13) as a function of range along the beam, at least two readings are necessary to get a three dimensioned wind vector. In one embodiment, each laser optics module 13 performs a conical scan through a full circle in the azimuth plane at each of three constant elevation angles, thereby to obtain a set of radial components of the air velocity. In the three-dimensioned space, in this non-limiting example, azimuth is measured clockwise from North at a specified time. In operation, this conical scanning method is advantageously repeated many times within a period long enough to sample a number of advecting eddies up to the largest scale of interest in a designated turbulent spectrum. From this scan, the processor module 15 readily models the wind profile within the three-dimensioned space the processor has defined around the landing zone.
In one non-limiting embodiment, the configuration of three LDV's measures wind velocity at various distances from the wind profiler device. The distances correspond to altitudes by distance multiplied by the sine of the angle of inclination of the laser in the LDV plus any inclination of the wind profiling device from horizontal. The wind velocity at that altitude parallel to the ground is equal to the measured wind velocity at that distance divided by the cosine of the angle of inclination of the laser in the LDV plus any inclination of the wind profiling device from horizontal.
In another non-limiting embodiment, the processor simply completes the wind profile and it is the profile that can be readily transmitted to an instrument within the aircraft to determine a suitable location from which to drop a payload based upon drop and sail characteristics of the payload. In another embodiment, the drop and sail characteristics of the payload are stored as a payload drop profile within the processor module 15 and the processor module 15 develops a release solution such that the exact release coordinates can be transmitted to the navigation avionics to direct the aircraft to the release point. Various additional embodiments are possible which allow ground determination of the wind profile to enable precise selection of coordinates from which to drop the payload.
Referring to
Beneath the sensors, in the non-limiting embodiment, power is provided by a battery and power supply module (“power module”) 4. As shown in
Within the laser optics modules 13 (only one shown for clarity), a source laser diode 134 generates the outgoing laser beam 101, which strikes a half-silvered mirror 132 splitting the beam such that the beam 101 exits through a focusing lens assembly 133 and then the Brewster window 131 described above. The outbound beam 101 is reflected by aerosols within winds in the three-dimensioned space to produce a return beam 103, which re-enters the Brewster window 131 passing through the focusing lens assembly 133 to strike the half-silvered mirror 132. At the half-silvered mirror 132, the returning beam is transmitted to a beam receiver 135. The original beam 101 also passed through the half silvered mirror 132 to strike a fully reflective mirror 136 to again strike the half-silvered mirror 132 to arrive with the inbound beam 103 at the receiver 135, there to create an interference pattern indicative of a radial speed of the aerosol. Thus the laser optics module 13 functions as a laser Doppler velocimeter.
While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, while a monostatic laser Doppler velocimeter is shown, a bistatic laser Doppler velocimeter might also be advantageously exploited. Bistatic laser optics systems derive their name from having separate transmit and receive optics. Monostatic systems have common transmit and receive optics. Bistatic systems have non-parallel transmit and receive beams that can be arranged to intersect at a certain point, thereby further accurately defining the remote probe volume (i.e., the area in space from which Doppler wind speed measurements are acquired). Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.
