Lighting-Ionosphere Coupling Workshop, LANL, 20 Aug 2008 Optical imaging of the mesosphere and ionosphere Jonathan J. Makela (University of Illinois)

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Overview Imaging as a remote sensing tool Estimating GW parameters in the mesosphere Observing structure and inferring pertinent parameters in the thermosphere/ionosphere –Airglow emissions of interest –Parameter estimation techniques Deployment considerations

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Why Imaging? Many methods exist to probe the upper atmosphere. Imaging provides several advantages over other techniques: –Large coverage area from a single site (650  650 km in mesosphere; 1750  1750 in thermosphere) –High spatial resolution (< km in mesosphere; ~km in thermosphere) –Good temporal resolution (~90 s  # filters used)

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Why Not Imaging? As with any observing method, there are also disadvantages, including: –Passive technique (rely on what Mother Nature gives us) –Measuring (height) integrated quantities –Difficulty in obtaining absolute quantities –Requirement of dark/clear skies There are many applications where the pros outweigh the cons and imaging is an appropriate technique to probe the upper atmosphere

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Airglow Chemilluminescent processes Chemistry determines altitude a given emission occurs at –Perturbations to the medium (AGWs, TIDs, etc) can modify the chemistry and are therefore observed as changes in emission intensity Visible from the ground with sensitive CCD cameras

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL OH (Hydroxyl) –Peak altitude ~88 km –Broad band emission (770 – 2000 nm) –Bright! O2 (Molecular Oxygen) –Peak altitude ~94 km –Narrow band emission (860 – 870 nm) Na (Sodium) –Peak altitude ~94 Km –Metal caused by meteor ablation –Used for resonance lidar OI (Atomic oxygen: Green Line) –Peak altitude ~98 km –Atomic line emission (557.7 nm) –Weakest of the three but most visible to human eye Prominent Airglows in Mesosphere

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Atmospheric Gravity Waves Transverse buoyancy waves –Transport energy across different regions of the atmosphere (one of the largest sources through mesospshere) –Perturbations modify mesospheric airglow emission intensities and can thus be imaged Pertinent parameters to know include: –Wave number (k h and k z ) –Intrinsic wave frequency (  i ) –Amplitude or perturbation (A or  ’/  )

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Single-Layer/Single-Site Observation Provides horizontal wave numbers and “true” frequency No vertical wavelength No intrinsic frequency –Need wind or vertical wavelength No amplitude –Requires vertical wavelength Airglow Layer

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Multi-Layer/Single Site Observation Vertical wavelength can be estimated by comparing phases in two different layers –Assumes known heights of layers Problems: –Wave does not always show up in two layers –Potential for 2  ambiguity Airglow Layers

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Single-Layer/Multi-Site Observation Provides multiple-angle observations of the same perturbation –Obtain z through standard tomography, tomography of Fourier Descriptors, or Parameter Estimation Airglow Layer Ph.D. work of D. Scott Anderson –Examined these techniques and their suitability to retrieving estimates of z

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Parameter Estimation If the goal of measurements is to infer a few parameters of AGWs, full-blown tomography is unnecessary –Parameter estimation can be performed using multi-site observations and an appropriate forward model without requiring the complexity of tomographic inversion –Significantly reduces computational requirements and improves end results

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Data Model G i is the result of a Gabor filter (a complex band pass filter) on the mapped pixel intensity data which selects the horizontal wavelength to be modeled where

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Phase Analysis (PE-Phase) If the layer centroid, z c, is assumed to be known this simplifies to a two-unknown problem Vertical wave number, k z, obtained from single-site observations of multiple layers Layer centroid obtainable from multi-site observations of a single layer Observed frequency,  t, is obtained from time sequence of images

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Amplitude Analysis (PE-mag) Amplitude of wave perturbation, A(x,y), obtained if imaging systems are well calibrated Layer thickness, , and vertical wave number, k z, obtainable Requires multi-site observations of a single (or multiple) layer(s)

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Example Experimental Campaign OH and OI imager Na lidar OH and OI imager Na lidar OH and OI imager

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Campaign Results Several wave packets observed in the different imagers Basic parameters obtained from the raw images alone Wave 1Wave 2

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Campaign Results Using the PE-phase technique, parameters are estimated –2  phase ambiguity leads to two solutions –Calculating winds from the dispersion relation tells us which direction is correct

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Campaign Results Collocated Na lidar measurements at UAO site confirm downward phase propagation

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Considerations PE-phase contains a 2  ambiguity –Can be mitigated by using the dispersion relation –Observing additional emission layers would also help on this front PE-mag (not shown) is heavily dependent on proper absolute calibration of each imager –Difficult to do as unknown atmospheric extinction is non-negligible and non-uniform –Can partially be mitigated by fitting PE-mag results to PE-phase results (for k z )

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Dissociative Recombination of O 2 + –Peak emission below the F peak –Narrow band emission (630.0 nm) –Chemistry depends on both electron and neutral densities –Long lifetime (~110 s) can cause blurring of features Radiative Recombination of O + –Peak emission at the F peak –Narrow band emission (777.4 nm) –Assuming an O + plasma, intensity is proportional to n e 2 –Prompt emission (no blurring) –Very dim emission Prominent Airglows in Thermosphere/Ionosphere

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Ionospheric “Topography” Using the combination of the height- dependent nm emission and density- dependent nm emission can give estimates of F-layer altitude and density

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Example from Sept 1999

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Example from Sept 1999

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Example from Sept 1999 “Bands” in radar data caused by gradients in electron density; higher densities to the south –Increase in density slightly before local midnight F layer is observed to decrease in altitude over time

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL F-Region Pedersen Conductivity Important parameter for understanding: – E- and F-region coupling –Instability processes (e.g., Perkins instability at mid-latitudes) nm volume emission rate is similar to the equation for Pedersen conductivity –Both can be shown to have dependence on n e and O 2  nm intensity is proportional to  P F

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Pedersen Airglow Technique Technique allows estimation of F-region Pedersen airglow over a large area (1000  1000 km) –Based on modeling study, RMS difference of mhos is expected (0.172 mhos if layer altitude is known)

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Comparison to ISR-derived  P F Technique validated against estimates of  P F derived from the Arecibo ISR Estimates were very good, especially given knowledge of the F-layer altitude

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Example During Mid-Latitude Event Evolution of structure at mid-latitudes typically understood as Perkins’ instabilities –Depends on variations in conductivities associated with altitude variations of the F layer that align from NW  SE

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Possibilities for Technique Improvements Uncertainties in techniques from: –Reliance on (climatological) background models –Imperfectly known absolute calibration and systematic factors (e.g., flat-fielding) –Unknown atmospheric extinction Improvements can be gained by either using better models (e.g., assimilative models) or actually integrating images as an assimilated data source –Initial work being performed to integrate into IDA4D

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Deployment Requirements Dark skies that are typically clear from cloud cover Availability of –power –facility for housing instrument –Internet connectivity For PE technique, need multiple sites separated by km viewing a common volume

20 Aug 2008Lightning-Ionosphere Coupling Workshop, LANL Summary Imaging of the mesosphere and thermosphere/ionosphere can lead to estimates of parameters important for understanding coupling processes –Provide observations of spatiotemporal dynamics over a large area Integrating images into assimilative models may resolve some of the short comings of current parameter estimation techniques