New modulation sequence for random-modulation continuous-wave lidar

Adam Rybaltowski*, Allen Taflove

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

1 Scopus citations


We propose and analyze a new modulation sequence for Random-Modulation Continuous-Wave (RM-CW) lidar. It is compared to known sequences (the M-, A1-, and A2-sequence), and shown to have significantly better, and nearly-ideal, signal properties. Namely, the cross-correlation function of this new sequence - named the AA1-sequence - consists of single peaks separated by zeros. Consequently, unlike the A1- and A2-sequence, it is immune to interference caused by backscattering from different ranges (e.g., due to clouds or irregularities in the aerosol distribution along the path of measurement). Also, since the demodulation sequence is balanced (i.e., consists of the same number of low and high chips), the new sequence, unlike the M-sequence, does not require the low laser output power to be zero to maintain desired cross-correlation properties; in lidar using a semiconductor laser as a transmitter, this would eliminate coupling between the demodulated signal amplitude and the emission wavelength, and thus facilitate wavelength-dependent (e.g., differential absorption, DIAL) measurements. Furthermore, we have calculated the post-demodulation signal-to-noise ratio in the presence of an additive noise of arbitrary power spectral density - it is applicable in all cases where the noise does not depend on the signal, which is typical in direct-detection mid-infrared lidar. The results show that in baseband transmission all these sequences have similar noise properties, except that the M-sequence - due to its imbalance property - has a much stronger near-zero-frequency noise pickup, which results in significantly worse noise performance in practical systems. Therefore, we claim that the new modulation sequence would yield superior performance in RM-CW lidar.

Original languageEnglish (US)
Pages (from-to)216-223
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2002
Externally publishedYes
EventLidar Remote Sensing for Industry and Environment Monitoring II - San Diego, CA, United States
Duration: Jul 30 2001Jul 31 2001


  • Mid-infrared lidar
  • Modulation sequence
  • Pseudo-random code
  • Random-modulation continuous-wave lidar

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


Dive into the research topics of 'New modulation sequence for random-modulation continuous-wave lidar'. Together they form a unique fingerprint.

Cite this