Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1999-10-27
2001-08-28
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005080, C356S342000
Reexamination Certificate
active
06281969
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of meteorology. More particularly the present invention relates to laser measurement of cloud base altitudes.
BACKGROUND OF THE INVENTION
There has been a long felt need for the capability to measure the base altitudes of one to three kilometers thick clouds as viewed from above. Conventional space-based lidar methods measure cloud depths by direct transmission of a laser beam through the cloud and sensing the backscattered returns. These techniques are limited by severe optical scattering by cloud particles to thickness less than 500 meters. Meteorological satellite images and Shuttle lidar data reveal transparent spaces even under dense cloud conditions. Representative albedos are diffuse reflectivities for cloud and surface features and are well known data from satellite meteorological measurements. Clouds are classified in various forms. Cumulonimbus clouds are thick and large with a 92% albedo. Stratus clouds are thick and usually over an ocean with a 64% albedo. Cirrus clouds are isolated clouds over land with a 36% albedo. Land features are also classified in various forms. Light sand including white sands has a 60% alebdo. Dark sands including sands in valleys, plains and slopes have a 27% albedo. Snow has a 59% albedo. Arctic summer ice has a 50% albedo. Coniferous forests have a 12% albedo. Oceans have a 7% albedo.
Current methods involve the propagation of a lidar beam from space through the full depth of the cloud. The strong backscattered radiation from the cloud aerosols indicates the presence of the cloud. A sharp drop off in the signal returns would signify the cloud bottom. Two problems exist with the conventional approach. The first problem is that thick clouds strongly attenuate light. Representative round-trip cloud extinctions are between 200 to 1000 dB per km. The second problem is multiple scattering from the cloud aerosols. This effect produces pulse stretching that prevents delineation of the sharp cloud bottom. These and other disadvantages are solved or reduced using the present invention.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for determining the altitude of the base of a cloud when viewed from above.
Another object of the invention is to provide a method for determining the altitude of the base of cloud by laser beam illumination through a clearing in a cloud formation and sensing returns through the clearing.
Another object of the invention is to provide a method for determining the altitude of the base of a cloud by laser beam illumination through a clearing in a cloud formation for a first reflection off the surface of the earth, a second reflection off the bottom base of the cloud, and a third reflection again off the surface and the earth, and sensing returns through the clearing.
The present invention is directed to a high altitude or space-based lidar method for the measurement of the altitude of a cloud base that is not restricted by cloud attenuation. The method relies upon cloud porosity and diffuse reflections from land or water features to sense cloud base bottoms from below. A lidar measurement system generates a beam of laser pulses that is communicated through a clearing in the cloud formation towards the surface of the earth. The beam first diffusely reflects off the earth surface to thereby scatter the beam. Some of the diffusely reflected laser light returns to the lidar system and can be sensed. A first portion of the scattered reflections is directed to a near by cloud formation. The first portion of scattered reflections is reflected off a cloud base of the cloud formation thereby creating a second portion of scattered returns. The second portion of the scattered returns is reflected back down towards the surface of the earth. The second portion of scattered reflections is again reflected off the surface of the earth creating a third portion of scattered reflected light that is returned to the measuring lidar system. The lidar system senses returns from the first and second reflections off the surface of the earth. The time differential between the first and second returns is used to compute the altitude of the cloud base. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.
REFERENCES:
patent: 4828382 (1989-05-01), Vermilion
Buczinski Stephen C.
Reid Derrick Michael
The Aerospace Corporation
LandOfFree
Cloud base measurement method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cloud base measurement method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cloud base measurement method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457841