E11 Tests of trace gas concentration multicomponent. monitoring system

Transcription

1 E11 Tests of trace gas concentration multicomponent remote monitoring system A.G. Berezin, S.L. Malyugin, A.I. Nadezhdinskii, D.Yu. Namestnikov, Ya.Ya. Ponurovskii, I.P. Popov, Yu.P. Shapovalov, D.B. Stavrovskii, I.E. Vyazov A. M. Prokhorov General Physics Institute of RAS 38 Vavilov str., Moscow, Russia.

2 Spectra of Several Molecules in Near Infrared Spectral Range l, m K, cm -1 /atm CO 2 * 1 HCl : 3 HF : 1 C 2 H 5 OH v, cm -1 CH 4 NH 3 Practically all molecules absorb in near IR spectral range where bands characteristic for C-H, N-H, O-H, etc. bonds are located. Open black cycles set of DLs available in our group.

3 Selection of analytical lines cm -1 KL, Absorption Absorption, a.u. Absorption, a.u Analytical line l= nm Analytical line l=162.5 nm cm l, m cm l, m NH Torr H 2 O - 1 Torr CO Torr H 2 O - 1 Torr Absorption, a.u Distance 6 m - H 2 O - 1 Torr - NH 3 -,23 Torr - CO 2 -,228 Torr - CH 4 -,12 Torr Analytical line l= nm cm l, m CH Torr H 2 O - 1 Torr l, m As one of applications, simultaneous detection of methane, ammonia, and CO 2 was considered. Example of analytical lines selection based on DL available and taking into account absence of interference with atmosphere water vapor absorption is shown.

4 System layout Layout example of trace gas multi-component remote monitoring system PD photo-diode, DL diode laser, FS fiber splitter, RC reference cell.

5 Receiving modules Family of receiving modules was used for different applications: 1. Handle - objective diameter 5 cm 2. Vehicle - objective diameter 1 cm 3. Helicopter - objective diameter 18 cm 1 2 3

6 Electronics View of multichannel electronics 1. Display and keyboard CO 2 CH 4 NH 3 2. NI PXI-131DC computer station 3. Three laser channels View of electronics of trace gas multi-component remote monitoring system (see separate poster). Three laser channels were used in present instrument to detect ammonia, methane and CO 2

7 Time multiplexing operation regime Signals, V NH 3 CH 4 CO 2 To increase selectivity of multiple molecular samples detection time multiplexing operation regime is used. Each laser operates at different time. Three upper graphs show signals recorded in three different reference laser channels. DL radiation from these three channels was combined in one single-mode fiber. Radiation from the fiber was collimated into parallel beam and directed to Topography Reflector (TR). Laser light scattered by TR was recorded by receiving module (lower graph) t, msec Simultaneous real time measurements of three molecules concentrations.

8 Noise of DL based systems G D i/i, 1/Гц 1E-11 1E-12 1E-13 1E-14 1E i, мкa Spectral density of photo-current relative noise as function of photo-current value (open cycles). Main physical mechanisms of DL based systems noise. 1. Thermal noise of preamplifier resistor (red) depends on pre-amplifier in use. 2. Photo-current shot noise (blue) depends on photocurrent value. 3. DL intensity quantum noise (green) is proportional to photo-current value. Total noise density is shown as thick line. For different photo-currents different noise type dominates. Resume: Noise in DL based systems is determined by photocurrent value.

9 Minimum detectable absorption As it was mentioned above, relative noise in DL based systems is determined by photo-current value - i. Portion of DL light scattered by TR and collected by receiving optics depends on A(q) - scattering diagram, L distance between instrument and TR, and D - receiving optics diameter. 1.E-1 1.E-2 i = P P i = A ( q ) 4 D 2 L 2 i MDA 1.E-3 1.E-4 P = 2 mw, di/dp = 1A/W, isotropic scattering with albedo =.4 1.E L/D Di/i - Minimum Detectable Absorption (MDA) as function of L/D. In present experiments L/D varied from 1 to 3. Main physical mechanisms of DL based systems noise - Di: 1. Thermal noise (red). 2. Photo-current shot noise (blue). 3. DL intensity quantum noise (green).

10 Allan plot 1.E-4 1.E-5 Absorption 1.E-6 1.E t, sec Allan plot of minimum detectable absorption as function of averaging time. This result was obtained for L/D = 1 (photocurrent shot noise dominated).

11 Long-term monitoring Sun, mv CO 2, ppm CH 4, ppm H 2 O, Torr /27/26 8/3/26 8/1/26 8/17/26 Water partial pressure variations Methane. Two intensive peaks are due to methane plume from power plant (3 km from GPI). CO 2 monitoring. Sun illumination. Example of one month simultaneous H 2 O, СН 4, and СО 2 concentrations monitoring.

12 Human presence remote detection C, ppm 4 35 C, ppm : 14: 15: 16: 17: 18: 19: 2: time 25 14:: 15:: 16:: 17:: time Example of remote detection of human appearance in controlled area (room 2) by measuring CO 2 concentration.

13 2D gas plume remote image Forest gas escape L Range pole Scanning 4 3 2CL, cm 2 Detector road Range pole 3 Y, m X, m -2 Using remote DL based system developed, methane concentration spatial distribution was measured in plume from calibrated leakage when forest was used as topography reflector.

14 Indoor test NH 3, ppm CH 4, ppm Indoor test. For test purpose the system was installed in DLS department corridor at 45 m distance from TR. Box with glass windows (car imitator) was installed in DL beam. CO 2, ppm 5 13: 14: 15: 16: 17: time 15:2 15:25 15:3 15:35 15:4 Simultaneous detection of methane (black), ammonia (red), and CO 2 (blue) when following samples volumes were injected in the box under investigation: СО 2 (99,96%) 5 liters; СН 4 (99,99%)-,5 liter; NH 3 (99,99%) -,1 liter. time

15 Outdoor test Concentration, ppm :21:14 16:22:5 16:22:57 16:23:48 16:24:4 time, hh:mm:ss NH3 Concentration, ppm CH4-5 16:28:48 16:29:32 16:3:13 16:3:55 16:31:36 16:32:18 time, hh:mm:ss Remote detection of ammonia and methane when sample gases were injected in vehicle located at 1 m from instrument. Fiber amplifiers were used to increase receiving signal.