# US 2010/0163733 A1 · Airborne tunable mid-ir laser gas-correlation sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2010/0163733 A1 - Document ID: US20100163733A1 - Status: Published application - Kind: A1 - Application number: 12/644,881 - Filed: 2009-12-22 - Published: 2010-07-01 - Earliest claimed: 2007-04-19 - Assignees: Science & Engineering Services, Inc. - Inventors: Coorg Rangaswamy Prasad; Bo Lin; Hyo Sang Lee - Web page: https://patentgrep.com/patent/US20100163733A1 ## CPC - G01N 21/3518: Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques - G01N 21/39: using tunable lasers - G01S 17/95: for meteorological use - G01N 2021/1795: {Atmospheric mapping of gases} - G01N 2021/3513: {Open path with an instrumental source} - Y02A 90/10: Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - Y02A: TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE ## Abstract A method and apparatus for measuring target gas concentrations in an atmosphere. The method and apparatus emit in the atmosphere a laser beam tuned to a molecular absorption line of a target gas, receive a reflected signal affected by gas absorption of the target gas in the atmosphere, divide and direct the received signal into a first optical path and a second optical path including in one of the paths a correlation gas cell filled with a predetermined concentration of the target gas, detect transmitted signals through the first optical path and the second optical path, and calculate a target gas concentration by comparing a first signal transmitted through the first optical path to a second signal transmitted through the second optical path. The apparatus includes a laser source tunable to a specific molecular absorption line of a target gas and configured to emit in the atmosphere a laser beam having a spectral bandwidth greater than a full width of the molecular absorption line of the target gas, a receiver configured to receive a reflected signal affected by gas absorption of the target gas in the atmosphere, and at least one detector configured to detect transmitted signals through the first optical path and the second optical path. ## Claims ### Claim 1 An apparatus for measuring target gas concentrations in an atmosphere, comprising: a laser source tunable to a molecular absorption line of a target gas, and configured to emit in the atmosphere a laser beam having a spectral bandwidth greater than a full width of the molecular absorption line of the target gas; and a receiver configured to receive a reflected signal affected by gas absorption of the target gas in the atmosphere, said receiver including, a first optical path and a second optical path, the second optical path including a correlation gas cell filled with a predetermined concentration of the target gas, and at least one detector configured to detect transmitted signals through the first optical path and the second optical path. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the laser source is configured to emit a laser beam having a spectral bandwidth that exceeds a combined width of a group of molecular absorption lines. ### Claim 3 (depends on 1) The apparatus of claim 1, further comprising: a processor configured to calculate a target gas concentration by comparing a first signal transmitted through the first optical path to a second signal transmitted through the second optical path. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the laser source comprises a pulsed laser source configured to produce a laser pulse having a pulse duration, and the processor is configured to time gate the received signal to capture an entirety of the laser pulse duration at the detector. ### Claim 5 (depends on 3) The apparatus of claim 3, wherein the processor is configured to derive a concentration of the target gas in the optical path based on Beer's law and an absorption strength of the target gas at a wavelength of the laser beam. ### Claim 6 (depends on 3) The apparatus of claim 3, wherein the processor is configured to accumulate a fixed number of measurements over a fixed time period. ### Claim 7 (depends on 1) The apparatus of claim 1, further comprising: an electronic filter disposed in an output of the detector, the filter configured to reject low frequency electronic signal components from the received reflected signal. ### Claim 8 (depends on 1) The apparatus of claim 1, further comprising: a telescope configured to provide a common field of view (FOV) for both the reference and gas correlation (off/on) channels. ### Claim 9 (depends on 1) The apparatus of claim 1, further comprising: multiple of said correlation cells in the second optical path filled with different target gases. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the correlation gas cell includes at least one of methane, ethane, carbon dioxide, carbon monoxide, and oxides of nitrogen. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein the correlation gas cell includes a simulant of the target gas. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein the first optical path includes a reference cell including air or including a gas different than the target gas. ### Claim 13 (depends on 1) The apparatus of claim 1, wherein the receiver comprises: a beam splitter configured to divide the received reflected signal into the first and second optical paths. ### Claim 14 (depends on 1) The apparatus of claim 1, wherein the laser source comprises a tunable mid IR laser source. ### Claim 15 (depends on 1) The apparatus of claim 1, wherein the laser source and the receiver comprises: a light detection and ranging unit configured to determine a distance of an object from the receiver. ### Claim 16 (depends on 1) The apparatus of claim 1, wherein the at least one detector comprises: a thermoelectrically cooled detector. ### Claim 17 (depends on 1) The apparatus of claim 1, further comprising: a mobile platform supporting the laser source and the receiver. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the mobile platform comprises a part of an aircraft. ### Claim 19 (depends on 17) The apparatus of claim 17, further comprising: a processor configured to calculate a target gas concentration for a plurality of optical paths between the aircraft and ground, and thereby produce an aerial mapping of a target gas concentration. ### Claim 20 (depends on 17) The apparatus of claim 17, wherein the mobile platform comprises a part of a landcraft. ### Claim 21 (depends on 1) The apparatus of claim 1, wherein said laser beam is configured to have a spectral bandwidth greater than 1-100 times the width of the molecular absorption line of the target gas. ### Claim 22 (depends on 1) The apparatus of claim 1, wherein said laser beam is configured to have a spectral bandwidth greater than 30-100 times the width of the molecular absorption line of the target gas. ### Claim 23 (depends on 1) The apparatus of claim 1, wherein said laser beam is configured to have a spectral bandwidth greater than 50 times the width of the molecular absorption line of the target gas.