# Presentation: 550073

## ALIAS Instrument Capabilities and Tracer Measurements

- Dr. Lance E. Christensen
- Dr. Christopher R. Webster
- Atmospheric Laser Spectroscopy Group
- Jet Propulsion Laboratory
- September 19, 2005

## ALIAS Characteristics

- Laser absorbance/2f detection, 80-m or 160-m pathlength.
- Four channels, broad spectral coverage:
- 1) Methane 		3.4 μm	IC laser
- 2) Water Isotopes	6.7 μm	QC laser
- 3) Water Isotopes	6.7 μm	QC laser
- 4) Water			1.9 μm	Near-IR laser
- Regulated inlet flow - isokinetic.
- 16 L sec-1 flow through instrument.
- Temperature of measured gas is regulated.

## Inlet/airflow

- Free-stream tap

- Inlet tap

**Inlet/airflow**

- Butterfly valve

**Differential pressure measurement at inlet.  Valve regulation of impedance.**

**Notes:**
190 lbs, < 70W, -4deg due to aircraft attitude

## Inlet/airflow

- Isokinetic flow

**Inlet/airflow**

**Notes:**
Neg. numbers mean pressure in inlet is less than free stream.
Some discussion is needed to translate diff pressure into something understandable to audience.

## Inlet/airflow

- Orifice-plate Flowmeter confirms flow through instrument

## Airflow/water signal.

- DEWAR

- No significant contamination from fore-optics.
- Herriott cell: 80-160m.  Near-IR laser: 0.14m

**Near-IR**

**Airflow/water signal.**

**Notes:**
Setup for next slide

## Airflow/water signal.

-  Virtually no end-to-end pressure difference.
-  Gas is well mixed throughout the analysis cell.
-  1/e residence time is 1.7 sec.

**Airflow/water signal.**

**Notes:**
Needed to establish that gas is well mixed, (therefore T sensor is indicative of whole cell, not just boundary layer in vicinity).

## Airflow/water signal.

- Very little evidence of significant water outgassing.

**Airflow/water signal.**

**Notes:**
Note that I use ‘ALIAS H2O signal’ rather than VMR.  This is because there are significant differences between instruments (HTW, JLH, ALIAS) in VMR.  Also, I don’t want to enter into the water measurement discussion – that is left to Chris on Tues.  If anyone asks, I’ll defer to Chris.

## Temperaure control

**Inlet: 150W heating**

**Spear: 500W heating**

**Temperaure control**

- All water particles are vaporized.

**Notes:**
I double checked these numbers on Sept. 14, 2005.

## Temperaure control

- Temperature is well regulated during flight.

**Temperaure control**

**Notes:**
Note that we regulated to 15 deg C, the T in the cell is 21.5 deg C +/- 1.  Some heating therefore occurs between last high wattage heater and inlet to cell.  If the heating occurs due to Herriott cell, then a lateral T gradient may exist.  I will not mention this.

## N2O

**N****2****O**

**Notes:**
Old measurements

## Carbon Monoxide

**Carbon Monoxide**

**Notes:**
I understand that this plot has pollution events removed and is higher (more than 2x?) than previous ALIAS-II measurements.  Lucien is aware of this.

## CH4

**CH****4**

**Notes:**
Old measurements

## CH4

- descent

- July 7, 2005
- descent

**CH****4**

**Notes:**
I really want to show methane data.  The anti-correlation between CH4 and altitude is somewhat disturbing.  Circles on top are a re-analysis using direct absorbance – verify that CH4 increase with altitude is not an artifact of 2f mis-calibration.  The bottom signal to noise is comparable to what I can find in the SOLVE and POLARIS notebooks.  The individual scans are 1.3 sec.

## Better Signal-to-Noise for water has been achieved.

- Shielding and filtering have been improved.

**WIIM**

## ALIAS employs a novel semi-conductor laser

- Dr. Rui Yang, (JPL)
- Interband Cascade Lasers (ICL):
-  Cover 2.5 to 5 μm spectral region.
-  High power.
-  Single-mode emission (DFB).
-  High efficiency (5-20mA threshold).
-  Progress towards room T devices.

**Notes:**
ICL’s differ from QC’s in that they are interband.  Low phonon loss results in more easily attained population inversions -> higher efficiency (hence the 10s of mA thresholds).

## Conclusions

- AVE-WIIF mission confirmed that ALIAS is:
- 	- Isokinetic
-  	- Isothermal
- 	- not contaminated by water outgassing
- Tracer sensitivities  (3 sec):
- CH4    	50 pptv
- N2O	60 pptv
- CO	300 pptv
-  ALIAS has integrated and employed IC Lasers.

**Notes:**
This needs a lot of work.