# Presentation: 873740

## Ground Based Lidar to Profile Tropospheric CO2 - Update 

** ****CO****2**** an important driver for climate change.  Currently only approximately half of the CO****2**** produced by man can be accounted for in the atmosphere and oceans, the rest is believed to have disappeared into terrestrial sinks whose location is not known to better than continental scale resolution. **
** ****Identifying location and size of sinks is crucial to understanding  their mode of operation and being able to characterize their long term behavior.   **
** ****Being able to measure CO****2**** concentrations within the planetary boundary layer provides a mechanism to locate sinks on both  local and regional scales.  **
** ****Combining measurements of CO****2****’s spatial and temporal variability with a transport model permits fluxes to be calculated.  **
**The fluxes can be used with an  inverse model to identify local and regional CO****2**** sinks.**
** ****Height resolved CO2 measurements are now made using tall  (typically TV) towers; **
** ****Generally <500 meters tall  with in-situ sensors capable of measuring CO****2**** at < 1ppmv precision.**

**Ground Based Lidar to Profile Tropospheric CO2 - Update**** **
**John Burris****1****, Arlyn Andrews****2****, Haris Riris****1****, Jim Abshire****3****, Amelia Gates****4****, Mike Krainak****5**** and Xiaoli Sun****1**
***1******Code 694, NASA Goddard Space Flight Center, Greenbelt, Md.  20771***
***Email: ***_[john.f.](mailto:john.f.burris@nasa.gov)__[burris](mailto:john.f.burris@nasa.gov)__[@](mailto:john.f.burris@nasa.gov)__[nasa](mailto:john.f.burris@nasa.gov)__[.](mailto:john.f.burris@nasa.gov)__[gov](mailto:john.f.burris@nasa.gov)_
***2******CMDL/NOAA, Boulder, Co. 80305***
***3****** Code 690, NASA Goddard Space Flight Center, Greenbelt, Md. 20771***
***4******GEST, UMBC, Baltimore, Md. 21250***
***5******Code 554, NASA Goddard Space Flight Center, Greenbelt, Md. 20771***
**Poster 4.2 - P**

** ****DIAL Lidar approach  in the 1572 nm CO2 absorption band**
** ****Measure backscatter profiles with laser tuned off & on a selected CO2 line.**
** ****Ratio of profiles yields extinction caused by CO****2**** absorption.**
** ****Measurement sensitive only to CO****2****.  On and off-line wavelengths separated by ~0.15 nm.**
** ****Fiber lasers leverage telecommunications technology. **
**  ****Pulse width ~100 ns;  Pulse rate 10 kHz for each wavelength**
** ****25 microsecond delay between each channel.  **
** ****Laser pulse energy: ~ 2-5 microjoules/pulse.**
**  ****Detector: InGaAs photon counting PMT. 4% quantum efficiency.**

**Goals**

** ****Develop & demonstrate a ground based CO****2**** profiling lidar, constructed from commercial parts, which can operate autonomously**
** ****Goal to measure height resolved CO****2**** profiles to top of boundary layer with a precision of 1 ppmv at least every hour.**
** ****Use differential absorption lidar (DIAL) technique.  This approach has been successfully employed in the measurement of stratospheric ozone to a precision of 1%.**
** ****Use micro-pulse lidar approach as a model - ie a compact, self-contained reliable & eyesafe  lidar capable of autonomous operation for months in remote locations**
** ****Cost goal per unit  <$200K.**** **
** ****Profiler’s measurements of C****O****2****’s**** spatial and temporal variability can be used with transport models to derive fluxes.  **
** ****Calibration and validation tool for field studies and space missions (eg OCO) cal/val.**

**Why Profile  ****CO****2**** from the Ground**

**Near Term Plans**

** ****Profiler can acquire data over a period of >4 hours unattended.  **
** ****Demonstrated ability to lock laser wavelengths to better than 1 pm, the resolution limit of the instrument making the measurement.  Goal is better than 0.5 pm.**
** ****10 kHz operation at each wavelength with 100 ns pulses.**

**Simulations of profiler measurement precision for  fiber laser (********) and optical parametric amplifier (+) for 10-minute signal averaging. **
**Aerosol backscatter coefficient ******** = 1.6*10****-7**** m****-1**** sr****-1****. **
** ****Fiber laser has 15 ********J per pulse.  **
**  ****OPA laser  has 150 ********J per pulse at 10 kHz**

**Calculated Performance**

** ****Smoothed on and offline range resolved aerosol returns.   Bin size = 30 m.**
** ****Online profile falls off more rapidly than offline profile . **
**Shows measurement of atmospheric CO2 extinction**

**Breadboard Profiling Lidar**

**Joint Workshop on NASA Biodiversity, Terrestrial Ecology, and Related Applied Sciences**

**August 21-25, 2006**

**Current Status**

** ****Test using two Mach-Zender modulators in series to better  extinguish leakage in transmitter.**
** ****Retrieve longer series of on & off-line  profile.**
** ****Calculate series of CO****2**** concentration profiles.**
** ****Evaluate performance of  Optical Parametric Amplifier based laser  (from ITT).  Expect higher per pulse energies.**
** ****Evaluate cooled  HgCdTe APDs as possible  replacement detectors.    Potentially higher QEs  at 1570 nm and  low noise. Rugged construction &  expect  longer lifetime . **

**Some Sample Measurements**

**The first peak is the online wavelength**
** ****Online profile has more counts because  DFB laser emits more power at this wavelength.**
** ****Fall off caused by interface between PBL&  free troposphere**

**ACKNOWLEDGEMENTS**
**We would like to gratefully acknowledge the support provided by NASA’s Tropospheric Chemistry Program, the Laser Risk Reduction Program and internal Goddard support including resources from the Earth Sciences Directorate.  Last but not least the support, collaboration and encouragement provided by the CO2 Sounder team headed by Dr. James Abshire is greatly appreciated.**

** ****Online (1571.111 nm) and **
**offline (1570.96 nm) profiles**
** ****6 minutes integration time. **