Optical Energy Variability Induced by Speckle: The Cases of MERLIN and CHARM-F IPDA Lidar

Cassé, Vincent; Gibert, Fabien; Édouart, Dimitri; Chomette, Olivier; Crévoisier, Cyril

doi:10.20944/preprints201907.0294.v1

Cited by 7 publications

(4 citation statements)

References 42 publications

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“…In this case, the outflow is likely to exist nonetheless (e.g. [23]). Thus the presence or not of a jet is certainly not an evidence of what really triggers the accretion, though it certainly puts some strong constraint on it.…”

Section: Some Key Problems About Jet Formationmentioning

confidence: 99%

“…For example, it requires high magnetic field strengths at the disk level (which have not been measured so far) and also a large magnetic lever arm is needed in order to obtain a terminal speed which is a few times the Keplerian speed ( ∼ < 10 5 km/s). Moreover, only a very small fraction of the accreted mass can be ejected at very high speeds, once a connection with a realistic disk structure is properly made [40,63,23]. By realistic disk structure we mean that in the accretion disk resistivity, turbulence and viscosity are taken into account within the hypothesis that the disk is pervaded by a large scale mean magnetic field.…”

Section: Magneto-centrifugal Acceleration From the Diskmentioning

confidence: 99%

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Jet Formation and Collimation

Sauty¹,

Tsinganos

Trussoni

Relativistic Flows in Astrophysics

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We briefly review our current understanding for the formation, acceleration and collimation of winds to jets associated with compact astrophysical objects such as AGN and µQuasars.All such outflows may be considered to a first approximation as ideal MHD plasmas escaping from a rotating and magnetized accretion disk with a magnetosphere around a central black hole. A crucial ingredient for a correct modelling of the steady state problem is to place the appropriate boundary conditions, by taking into account how information can propagate through the outflow and ensuring, e.g., that shocks produced via the interaction of the flow with the external medium do not affect the overall structure. As an example underlining the role of setting the correct boundary conditions, we make the analogy of the critical surfaces in the steady and axisymmetric MHD problem with the event horizon and ergosphere of a rotating black hole in relativity.We discuss the acceleration of the outflow, by gas, radiation, or wave pressure gradients and also by magnetic mechanisms, showing the important role played by the disk corona in the vicinity of the black hole. Pressure and magnetic confinement both may also play a role in confining the outflow, although magnetic hoop stress confinement is likely to be a rather dominant process in tightly collimated outflows. The possible asymptotical morphology that jets achieve and the instabilities which are likely to explain the observed structures but do not prevent jets to possess toroidal magnetic fields are also reviewed.Finally, it is proposed that in a space where the two main variables are the energy of the magnetic rotator and the angle between the line of sight and the ejection axis, some observed characteristics of AGN jets can be understood. A criterion for the transition of the morphologies of the outflows from highly collimated jets to uncollimated winds is given. It is based on the analysis of a particular class of exact solutions and may somehow generalize other earlier suggestions, such as the spinning of the black hole, the fueling of the central object, or the effects of the environment.Thus, while the horizontal AGN classification from Type 0 to Types 1 and 2 may well be an orientation effect -i.e. a dependence on the viewing angle between the source axis and the observer as in the standard model -the vertical AGN classification with uncollimated outflows (radio-quiet sources) and collimated outflows (radio-loud sources) depends both, on the efficiency of the magnetic rotator and the environment in which the outflows propagate.

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Section: Some Key Problems About Jet Formationmentioning

confidence: 99%

Section: Magneto-centrifugal Acceleration From the Diskmentioning

confidence: 99%

Jet Formation and Collimation

Sauty¹,

Tsinganos

Trussoni

Relativistic Flows in Astrophysics

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show abstract

“…Zero-path calibration indicates that the speckle limited noise floor of the DAOD measurement is limited to ∼ 0.005 over a half second average (250 shots per wavelength), where additional averaging provides further reduction. A recent MERLIN study (Cassé et al, 2019) showed that the impact of speckle on transmit energy measurements scales with SNR and that the expected random noise due to speckle for MERLIN approached ≤ 5 ppb (or ∼ 0.25 % for 2000 ppb) with < 10 s of averaging. These values are in line with HALO's findings and indicate the potential for speckle to dominate measurement noise if not accommodated for.…”

Section: Xch 4 Retrievalmentioning

confidence: 99%

Evaluation of the High Altitude Lidar Observatory Methane Retrievals During the Summer 2019 ACT-America Campaign

Barton-Grimley

Nehrir

Kooi

et al. 2022

Preprint

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Abstract. The NASA Langley Research Center High Altitude Lidar Observatory (HALO) is a multi-function and modular lidar developed to address the observational needs of NASA’s weather, climate, carbon cycle, and atmospheric composition focus areas. HALO measures atmospheric H2O mixing ratios, CH4 mole fractions, and aerosol/cloud optical properties using the Differential Absorption Lidar (DIAL) and High Spectral Resolution Lidar (HSRL) techniques, respectively. In 2019 HALO participated in the NASA Atmospheric Carbon and Transport – America campaign on board the NASA C-130 to compliment a suite of greenhouse gas in-situ sensors and provide, for the first time, simultaneous measurements of column CH4 and aerosol/cloud profiles. HALO operated in 18 of 19 science flights where the DIAL and Integrated Path Differential Absorption lidar (IPDA) techniques at 1645 nm were used for column and multi-layer measurements of CH4 mole fractions, the HSRL and backscatter techniques at 532 and 1064 nm, respectively, for retrievals of aerosol backscatter, extinction, depolarization, and mixing layer heights. In this paper we present HALO’s measurement theory for the retrievals of column and multi-layer XCH4, retrieval accuracy and precision including methods for bias correction, and a comprehensive total column XCH4 validation comparison to in-situ observations. Comparisons of HALO XCH4 to in-situ derived XCH4, collected during spiral ascents and descents, indicates mean difference of 2.54 ppb and standard deviation of the differences of 16.66 ppb when employing 15 s along track averaging (< 3 km). A high correlation coefficient of R = 0.9058 was observed for the 11 in-situ spiral comparisons. Column XCH4 measured by HALO over regional scales covered by the ACT-America campaign are compared against in-situ CH4 measurements carried out within the planetary boundary layer (PBL) from both the C-130 and B200 aircraft. Favorable correlation between the in-situ point measurements within the PBL and the remote column measurements from HALO elucidates the sensitivity of a column integrating lidar to CH4 variability within the PBL, where surface fluxes dominate the signal. Novel capabilities for CH4 profiling in regions of clear air using the DIAL technique are presented and validated for the first time. Additionally, profiling of CH4 is used to apportion the PBL absorption from the total column and is compared to previously reported IPDA cloud slicing techniques that estimate PBL columns using strong echoes from fair weather cumulus. The analysis presented here points towards HALO’s ability to retrieve accurate and precise CH4 columns with the prospects for future multi-layer profiling in support of future suborbital campaigns.

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Section: Xch 4 Retrievalmentioning

confidence: 99%

Evaluation of the High Altitude Lidar Observatory (HALO) methane retrievals during the summer 2019 ACT-America campaign

et al. 2022

View full text Add to dashboard Cite

Abstract. The NASA Langley Research Center High Altitude Lidar Observatory (HALO) is a multi-functional and modular lidar developed to address the observational needs of NASA's weather, climate, carbon cycle, and atmospheric composition focus areas. HALO measures atmospheric H2O mixing ratios, CH4 mole fractions, and aerosol/cloud optical properties using the differential absorption lidar (DIAL) and high-spectral-resolution lidar (HSRL) techniques. In 2019 HALO participated in the NASA Atmospheric Carbon and Transport – America campaign on board the NASA C-130 to complement a suite of greenhouse gas in situ sensors and provide, for the first time, simultaneous measurements of column CH4 and aerosol/cloud profiles. HALO operated in 18 of 19 science flights where the DIAL and integrated path differential absorption (IPDA) lidar techniques at 1645 nm were used for column and multi-layer measurements of CH4 mole fractions, and the HSRL and backscatter techniques were used at 532 and 1064 nm, respectively, for retrievals of aerosol backscatter, extinction, depolarization, and mixing layer heights. In this paper we present HALO's measurement theory for the retrievals of column and multi-layer XCH4, retrieval accuracy, and precision including methods for bias correction and a comprehensive total column XCH4 validation comparison to in situ observations. Comparisons of HALO XCH4 to in situ-derived XCH4, collected during spiral ascents and descents, indicate a mean difference of 2.54 ppb and standard deviation (SD) of the differences of 16.66 ppb when employing 15 s along-track averaging (<3 km). A high correlation coefficient of R=0.9058 was observed for the 11 in situ spiral comparisons. Column XCH4 measured by HALO over regional scales covered by the ACT-America campaign is compared against in situ CH4 measurements carried out within the planetary boundary layer (PBL) from both the C-130 and B200 aircraft. Favorable correlation between the in situ point measurements within the PBL and the remote column measurements from HALO elucidates the sensitivity of a column-integrating lidar to CH4 variability within the PBL, where surface fluxes dominate the signal. Novel capabilities for CH4 profiling in regions of clear air using the DIAL technique are presented and validated for the first time. Additionally, profiling of CH4 is used to apportion the PBL absorption from the total column and is compared to previously reported IPDA cloud slicing techniques that estimate PBL columns using strong echoes from fair weather cumulus. The analysis presented here points towards HALO's ability to retrieve accurate and precise CH4 columns with the prospects for future multi-layer profiling in support of future suborbital campaigns.

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Optical Energy Variability Induced by Speckle: The Cases of MERLIN and CHARM-F IPDA Lidar

Cited by 7 publications

References 42 publications

Jet Formation and Collimation

Jet Formation and Collimation

Evaluation of the High Altitude Lidar Observatory Methane Retrievals During the Summer 2019 ACT-America Campaign

Evaluation of the High Altitude Lidar Observatory (HALO) methane retrievals during the summer 2019 ACT-America campaign

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