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An interpolation method is described for range measurements of high precision altimetry with repeating intensity modulated continuous wave (IM-CW) lidar waveforms using binary phase shift keying (BPSK), where the range profile is determined by means of a cross-correlation between the digital form of the transmitted signal and the digitized return signal collected by the lidar receiver. This method uses reordering of the array elements in the frequency domain to convert a repeating synthetic pulse signal to single highly interpolated pulse. This is then enhanced further using Richardson–Lucy deconvolution to greatly enhance the resolution of the pulse. We show the sampling resolution and pulse width can be enhanced by about two orders of magnitude using the signal processing algorithms presented, thus breaking the fundamental resolution limit for BPSK modulation of a particular bandwidth and bit rate. We demonstrate the usefulness of this technique for determining cloud and tree canopy thicknesses far beyond this fundamental limit in a lidar not designed for this purpose.

Frontal boundaries have been shown to cause large changes in CO2mole‐fractions, but clouds and the complex vertical structure of fronts make these gradients difficult to observe. It remains unclear how the column average CO2dry air mole‐fraction (XCO2) changes spatially across fronts, and how well airborne lidar observations, data assimilation systems, and numerical models without assimilation capture XCO2frontal contrasts (ΔXCO2,i.e., warm minus cold sector average of XCO2). We demonstrated the potential of airborne Multifunctional Fiber Laser Lidar (MFLL) measurements in heterogeneous weather conditions (i.e., frontal environment) to investigate the ΔXCO2during four seasonal field campaigns of the Atmospheric Carbon and Transport‐America (ACT‐America) mission. Most frontal cases in summer (winter) reveal higher (lower) XCO2in the warm (cold) sector than in the cold (warm) sector. During the transitional seasons (spring and fall), no clear signal in ΔXCO2was observed. Intercomparison among the MFLL, assimilated fields from NASA's Global Modeling and Assimilation Office (GMAO), and simulations from the Weather Research and Forecasting‐—Chemistry (WRF‐Chem) showed that (a) all products had a similar sign of ΔXCO2though with different levels of agreement in ΔXCO2magnitudes among seasons; (b) ΔXCO2in summer decreases with altitude; and (c) significant challenges remain in observing and simulating XCO2frontal contrasts. A linear regression analyses between ΔXCO2for MFLL versus GMAO, and MFLL versus WRF‐Chem for summer‐2016 cases yielded a correlation coefficient of 0.95 and 0.88, respectively. The reported ΔXCO2variability among four seasons provide guidance to the spatial structures of XCO2transport errors in models and satellite measurements of XCO2in synoptically‐active weather systems. First airborne observations of column average CO2dry‐air mole‐fraction (XCO2) changes across fronts observed during ACT‐A are reportedXCO2frontal structures compare reasonably well with Weather Research and Forecasting—Chemistry and an in situ data driven assimilation systemResults reveal that the differences across models and data were generally much smaller than the magnitude of XCO2frontal contrasts First airborne observations of column average CO2dry‐air mole‐fraction (XCO2) changes across fronts observed during ACT‐A are reported XCO2frontal structures compare reasonably well with Weather Research and Forecasting—Chemistry and an in situ data driven assimilation system Results reveal that the differences across models and data were generally much smaller than the magnitude of XCO2frontal contrasts

An interpolation method is described for range measurements of high precision and altimetry using repeating intensity-modulated continuous wave (IM-CW) lidar waveforms, where the range is determined by means of a cross-correlation between the digital form of the transmitted signal and the digitized return signal collected by the lidar receiver. This method uses reordering of the array elements in the frequency domain to convert a repeating synthetic pulse signal to single highly interpolated pulse. The computation of this processing is marginally greater than the correlation itself, as it only involves reordering of the correlation in the frequency domain, which makes it possible to implement this in a real time application. It is shown through theoretical arguments and flight-testing that this is a viable method for high-speed interpolated range measurements. Standard deviation is 0.75 m over water with only 350 mw of transmitted power at 2600 m.

In this theoretical study, modulation techniques are developed to support the Active Sensing of CO_2 Emissions over Nights, Days, and Seasons (ASCENDS) mission. A continuous wave (CW) lidar system using sine waves modulated by maximum length (ML) pseudo-noise (PN) codes is described for making simultaneous online/offline differential absorption measurements. Amplitude and phase-shift keying (PSK) modulated intensity modulation (IM) carriers, in addition to a hybrid-pulse technique are investigated, which exhibit optimal autocorrelation properties. A method is presented to bandwidth limit the ML sequence based on a filter implemented in terms of Jacobi theta functions, which does not significantly degrade the resolution or introduce sidelobes as a means of reducing aliasing and IM carrier bandwidth.

A system using a nonlinear multiswept sine wave is described, which employs multichannel multiswept orthogonal waves, to separate channels and make multiple, simultaneous online/offline CO_2 measurements. An analytic expression and systematic method for determining the orthogonal frequencies for the unswept, linear swept, and nonlinear swept cases is presented. It is shown that one may reduce sidelobes of the autocorrelation function while preserving cross channel orthogonality, for thin cloud rejection.