Phase sensing and scanning time of flight LADAR using atmospheric absorption bands
View Patent ↗A phase-sensing and scanning time-of-flight LADAR method and device are disclosed that take advantage of an atmospheric absorption bands within the solar IR spectrum. In the phase-sensing LADAR embodiment, an object is illuminated with electromagnetic energy such as a laser beam having a wavelength substantially equal to a predetermined atmospheric absorption band such as 1.39 microns. The transmitted laser beam is modulated at a predetermined frequency and has a first phase. The phase of the reflected and returned laser beam is altered proportional to the distance of the object and has a second phase. The first phase of the transmitted signal and the second phase of the received signal are compared and used to determine the distance of the object from the device. The system may comprise a modified laser that is tuned to operate in an atmospheric absorption band. A method to identify range ambiguity is disclosed by periodically altering the modulation frequency from a first modulation frequency to a second modulation frequency. In the scanning LADAR embodiment, an object is scanned or illuminated with electromagnetic energy having a wavelength substantially equal to a predetermined atmospheric absorption band at a first time and detects the reflection of the beam at a second time. The difference in time from the transmission of the scanning beam and the detection of the reflection of the beam from the object is used to calculate the range of the object.
1. A method for determining the range of the surface of an object comprising the steps of:
selecting an atmospheric absorption band in the solar near-IR region defining a solar transmission hole having a predetermined electromagnetic energy absorption characteristic to define a predetermined atmospheric absorption band wavelength,
providing an electromagnetic beam having a wavelength substantially equal to the predetermined atmospheric absorption band wavelength,
modulating the electromagnetic beam at a predetermined frequency to define a transmitted sine wave having a first phase,
illuminating at least a portion of the surface of the object with the transmitted sine wave to define a reflected sine wave having a second phase,
electronically receiving the reflection of at least a portion of the reflected sine wave from the surface of the object,
calculating the difference in phase between the first phase and the second phase to determine the range of the object.
2. The method of claim 1 wherein the wavelength is about 1.39 microns.
3. The method of claim 1 wherein the electromagnetic beam is the output of a tuned laser element.
4. The method of claim 1 further comprising periodically alternating the modulation frequency from a first modulation frequency to a lower second modulation frequency at a predetermined interval to determine a range ambiguity.
5. A method for determining the range of the surface of an object comprising the steps of:
selecting an atmospheric absorption band in the solar near-IR region defining a solar transmission hole having a predetermined electromagnetic energy absorption characteristic to define a predetermined atmospheric absorption band wavelength,
scanning at least a portion of the surface of an object with an electromagnetic beam having a wavelength substantially equal to the predetermined atmospheric absorption band wavelength at a first time to define a transmission beam,
electronically receiving the reflection of at least a portion of the transmission beam from the surface of the object to define a second time,
calculating the difference between the first time and the second time to determine the range of the object.
6. The method of claim 5 wherein the wavelength is about 1.39 microns.
7. The method of claim 5 wherein the electromagnetic beam is the output of a tuned laser element.