Microaltimeter

• US 6,343,245 B1
• Filed: 04/06/2000
• Issued: 01/29/2002
• Est. Priority Date: 04/14/1999
• Status: Expired due to Fees

• Current Assignee: U.S. Government
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Degnan, John J
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Donnelly, Arthur D.
• Application Number:
  US09/544,169
• Time in Patent Office: 663 Days
• Field of Search: 701/4, 701/223, 701/3, 356/336, 356/337, 250/208.1, 244/164, 244/171
• US Class Current: 701/4
• CPC Class Codes: G01C 5/005 altimeters for aircraft G01C5/02, G01C5/06 take precedence
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications

Abstract

A microaltimeter measures altitude or range highly accurately from an orbiting vehicle. The microaltimeter has a low power solid state laser that is pulsed at a rate above 1 kilohertz. The pulses are delivered to a small telescope which sends them to a planetary surface and receives return reflections. A high efficiency photon detector measures received photons and supplies received photon signals to a process or which makes a time-based bin-wise comparison to find the time of flight and hence the range.

Claims

1. Apparatus for measuring accurately the altitude of an aircraft or a spacecraft, comprising:

a low power source of pulse coherent light;

a telescope that receives the pulses of light and collimates them prior to emission;

a high efficiency photon detector emitting detection signals responsive to the number of reflected photons received from a surface; and

,

a processor system responsive to signals from a high efficiency photon detector and producing a ranging signal in response thereto, by storing successive signals in range basis and verifying the return time of flight of photon when adjacent beam values are in a predetermined relationship wherein said processor system determines whether the contents of the adjacent basis are similar.

2. A microaltimeter for measuring accurately the altitude of an aircraft or a spacecraft according to claim 1 wherein said source of light in a low power loses emitter pulses at a rate greater than one kilohertz.

3. Apparatus according to claim 1 wherein said laser is a Q-switched solid state laser producing visible light pulses having a duration of less than one monosecond.

4. Apparatus according to claim 1 wherein said telescope is a small diameter telescope which provides a nominal laser photon to solar background signal-to-noise ratio of less than one.

5. Apparatus according to claim 1 wherein the high efficiency photon detector produces output signals in response to each photon received to provide a photon time of flight signal.

6. Apparatus according to claim 1 further composing a spatial filter for removing off-axis photons from a received photon stream.

7. Apparatus according to claim 1 function comprising a spatial filter for removing a portion of the solar background photons received by the telescope.