Active Optical Sensors Breakout Session



Active Optical Sensors Breakout Session

The following are notes from the Active Optical Sensors breakout session. The notes below are a first attempt to capture the key points of the discussion. The notes were compiled quickly during and immediately after the session and are not well-organized or complete. We would appreciate the opportunity to edit any document that uses these notes as inputs. - John Hair and Chris Hostetler (NASA LaRC).

Lidars Called for In Mission Sessions

Cloud and Aerosol Mission

• Water vapor lidar

• High Spectral Resolution Lidar (HSRL) (for clouds and aerosol)

• Ozone (this capability was missed in the mission summary but was required in the mission described in the July 2004 workshop)

Active Fires/Emissions Mission

• High Spectral Resolution Lidar (cloud/aerosol)

• Ozone lidar (this capability was missed in the mission summary but was required in the mission described in the July 2004 workshop)

Hurricane Mission

• Water vapor lidar

• High Spectral Resolution Lidar (HSRL) (for clouds and aerosol)

• Winds (long range)

Carbon Mission

• CO2 lidar

• Winds (short range)

Vegetation Mission

• Waveform lidar (canopy top)

Common Themes

General

• Ozone combined with aerosol lidar (HSRL) as a single unit to take advantage of common laser, telescope, and data acquisition elements (discussed at July 2004 workshop))

• Ozone, water vapor, aerosol and long-range wind lidars fly at relatively high altitude (40-60 kft)

• CO2, topographical, vegetation canopy, and short-range winds lidar fly at lower altitudes (100 ft – 40 kft)

Common Technology Themes

• Miniaturization is required (telescope, lasers, detection/data acquisition electronics)

• Thermal control

o Laser cooling/heating

o Window frosting

o Cold soaking and condensation on optics

• Contamination control (dust)

• Autonomy

o Currently trending to systems that are more “turn-key” but need work to get there

o Housekeeping data transmitted to ground station

o Science data transmitted to ground station; may require real-time on-board processing to reduce data rate to reasonable level. Autonomous data processing can be extremely difficult; work needed in this area.

Technology Development Areas

Ozone, Water Vapor, and HSRL (plus potentially direct detection winds)

• Common Nd:YAG pump/transmitter (this technology is currently being developed)

o Single longitudinal mode, tunable over Nd:YAG gain curve, frequency stable

o M2 < 1.5

o Energy > 100 mJ to the fundamental (1064 nm)

o Accommodations

▪ Size: 2 x 8 x 11 inches

▪ Mass: 30 lbs

▪ Input power: 0.5 kW

• Frequency conversion

o Optical Parametric Oscillator required for ozone DIAL application. This is currently under development under the Laser Risk Reduction Program; development promising but needs some further work and testing.

o Nd:YAG-pumped Ti:Saphire required for water vapor application. This has been done for pressurized aircraft by DLR in Germany. No work currently funded in the US.

• Common Receiver Technology

o Telescope design/fabrication techniques. The telescope dominates the volume of the mission. The telescope may have to conform to an awkward volume as imposed by the vehicle. A greater aperture and packing density of system components (plus other instruments) may be achieved if the telescope can be made of arbitrary aperture shape (e.g., square instead of circular). Also telescope will have to be fast to maintain a small volume (i.e., to minimize length along the optical axis). Current diamond turning techniques for all-metal mirrors may allow the construction of fast optics of arbitrary pupil shape. Need work in this area to determine performance of diamond-turned metal optics in the visible and UV wavelengths.

o Telescope area >= 200 in2 (16-inch diameter)

o Filter technology. Require narrowband filters for rejection of reflected sunlight (i.e., noise). Bandwidths in the 10-100 pm range.

• Specific Receiver Technology

o Interferometric 355 nm HSRL receiver module. Only crude ground-based demonstrations have been accomplished in the past.

o Seed laser for Nd:YAG pump/transmitter. Must be compact, rugged, and tunable over the Nd:YAG gain profile. Must also have enough energy to double to 532 nm and preferably triple to 355 nm. Some technology being developed under SBIRs; looks promising but needs further work.

• Data acquisition and control electronics

o Compact, high dynamic range digitizers and hardware data averagers are not available and will have to be developed to reduce volume, mass, and power.

o Common control and data archiving electronics tailored to the lidar application required to reduce volume, mass, and power. (Not a low TRL level, but development still required.)

o

Winds (Long Range, Pulsed, scanning)

• Transmitter

o Energy: 200mJ at 2um, 10Hz

o Electrical: 200W

o Vol: 300 in3

o Mass: 30 #(?)

• Receiver

o Wedge scanner, M2 < 1.5

o Area ~200 in2 (0.4 m)

Winds (Short Range, CW, fixed range)

• Transmitter

– Energy: 5mJ at 2um, 100Hz, fiber

– Electrical: 150W

– Vol: 200 in3

– Mass: 15 #(?)

• Receiver

– Wedge scanner, M2 < 1.5

– Area ~50 in2 (0.1 m)

Cost and Development Time

|Instrument |WAG Cost |Time |Time to Demo (Less than |

| | | |full capa) |

|O3+Aerosol (Backscatter) |$7M |4-5 years |2-3 years |

|HSRL |$5M |4 years |2-3 years |

|H2O |$7M |5 years |4 years |

|O3+HSRL |$8M |4-5 years |  |

|O3+HSRL+H2O |$9M |5 years |  |

|Winds (long range, pulsed,scanning) |$10M |5 years |  |

|Winds (short range, CW) |$5M |3 years |  |

|CO2 (1%) |$10M |5 years |  |

Technology and Development Gaps

• Very little water vapor lidar transmitter development ongoing at this time. Funding needed in this area.

• Inteferrometric HSRL receiver technologies are not being developed in the US. Work ongoing in Europe, but insight into progress and problems difficult to obtain.

Trends

Volume, mass, and power required for lidars are generally decreasing due to the increased use of diode-pumped lasers and advances in receiver and data acquisition technologies.

Systems meeting some of the requirements outlined here-in have been proposed to technology development programs (e.g., IIP); however, no awards have been made in this area. Efforts to date have largely been “bootlegged” using Director’s Discretionary Funding and money contributed by other programs. Stable funding is required to develop robust technologies and instruments for the UAV applications described here.

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