Fast, High Resolution 3-D Flash LADAR Imager
A device and method for LADAR ranging using relatively long laser pulse widths and slower system clock speeds is provided. The center points of the sent and received laser signal such as Gaussian laser pulses are identified by time sampling the sent and received laser signal waveforms at predetermined time positions. The signal energy within each time sample of the respective sent and received laser signals defines a clock “bin”. The received laser signal generates an output from a photodetector cell on a focal plane array that is converted into voltage. The signal energy is integrated using a capacitor array for each of the clock bins and is representative of the signal energy in each time sample. The output of the capacitor array is collected in buffer and digitized. Signal processing means extracts the center of the transmitted and received pulses and the time-of-flight calculated as the time between the transmitted and returned centers of the laser signal pulses.
1 . A method for determining the center point of a pulse of an electromagnetic signal comprising the steps of:
time sampling the signal energy of a pulse of an electromagnetic signal at a predetermined number of time positions to define a predetermined number of clock bins,
calculating the signal energy within each clock bin, and,
performing an autocorrelation function to interpolate between a predetermined number of clock bins to determine the center of the pulse.
2 . The method of claim 1 wherein the signal energy calculation comprises an integration function.
3 . A method for determining the center point of a pulse of an electromagnetic signal comprising the steps of:
time sampling the signal energy of a pulse of an electromagnetic signal at a predetermined number of time positions to define a predetermined number of clock bins,
calculating the signal energy within each clock bin, and,
performing a curve fitting function to interpolate between a predetermined number of clock bins to determine the center of the pulse.
4 . The method of claim 3 wherein the signal energy calculation comprises an integration function.
5 . The method of claim 3 where the curve-fitting function comprises an erf function.
6 . A method for determining the range of a target surface comprising the steps of:
imaging a target surface with a first electromagnet signal having a substantially Gaussian pulse temporal distribution,
receiving a second reflected electromagnetic signal having a substantially Gaussian pulse temporal distribution from the target surface,
time sampling the signal energy of the first and second electromagnetic signals at a predetermined number of time positions to define a predetermined number of clock bins for each of the first and second electromagnetic signals,
calculating the signal energy within each clock bin,
performing an autocorrelation to interpolate between a predetermined number of clock bins of the first electromagnetic signal and performing an autocorrelation to interpolate between a predetermined number of clock bins of the second electromagnetic signal to determine the center of the first and second electromagnetic pulses, and,
determining the time difference between the centers of the first and second electromagnetic signals.
7 . The method of claim 6 wherein the signal energy calculation comprises an integration function.
8 . A method for determining the range of a target surface comprising the steps of:
imaging a target surface with a first electromagnet signal having a substantially Gaussian pulse temporal distribution,
receiving a second reflected electromagnetic signal having a substantially Gaussian pulse temporal distribution from the target surface,
time sampling the signal energy of the first and second electromagnetic signals at a predetermined number of time positions to define a predetermined number of clock bins for each of the first and second electromagnetic signals,
calculating the signal energy within each clock bin,
performing a curve fitting function to interpolate between a predetermined number of clock bins of the first electromagnetic signal and performing a curve fitting function to interpolate between a predetermined number of clock bins of the second electromagnetic signal to determine the center of the first and second electromagnetic pulses, and,
determining the time difference between the centers of the first and second electromagnetic signals.
9 . The method of claim 8 wherein the signal energy calculation comprises an integration function
10 . A method for determining the range of a target surface comprising the steps of:
imaging a target surface with a first electromagnet signal having a substantially Gaussian pulse temporal distribution,
receiving a second reflected electromagnetic signal having a substantially Gaussian pulse temporal distribution from the target surface,
time sampling the signal energy of the second electromagnetic signal at a predetermined number of time positions to define a predetermined number of clock bins for second electromagnetic signal,
calculating the signal energy within each clock bin,
providing a weighting factor based an expected second electromagnetic signal,
performing a convolution on the second electromagnetic signal using the weighting factor to determine its center, and,
determining the time difference between the centers of the first and second electromagnetic signals.
11 . The method of claim 10 wherein the signal energy calculation comprises an integration function