On the surface apparent reflectance exploitation: Entangled Solar Induced Fluorescence emission and aerosol scattering effects at oxygen absorption regions

2020 ◽  
Author(s):  
Neus Sabater ◽  
Pekka Kolmonen ◽  
Luis Alonso ◽  
Jorge Vicent ◽  
José Moreno ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
A Priori ◽  
European Space Agency ◽  
High Spectral Resolution ◽  
Oxygen Absorption ◽  
Aerosol Scattering ◽  
Scattering Effects ◽  
Spectrally Resolved ◽  
Absorption Features ◽  
Aerosol Characterization

<p>Monitoring vegetation photosynthetic activity and its link with the carbon cycle at a global scale is a leading breakthrough that the scientific community has been seeking in recent years. Pursuing this goal, one of the most important advances in the last decade has been the measurement of the Solar Induced Fluorescence (SIF) at a satellite scale. Current satellite-derived SIF estimations provide SIF measured at certain specific wavelengths depending on the retrieval strategy and the instrument capabilities. However, for the time being, no global observations of the total spectrally resolved and integrated SIF signal have been yet achieved. In a near-future context, spectrally resolved SIF estimations will be provided by missions such as the FLuorescence EXplorer (FLEX) from the European Space Agency.</p><p>When disentangling the total SIF contribution, emitted between 650-800 nm, from the acquired satellite signal, molecular and aerosol absorption and scattering effects must be carefully accounted for.  Particularly, within the oxygen absorption features, the characterization of the aerosol scattering effects represents the most critical step prior to the SIF estimation.</p><p>In the context of the FLEX/Sentinel-3 tandem mission concept, this work presents a novel technique that refines any a priori aerosol characterization process through the exploitation of the high spectral resolution surface apparent reflectance signal at the oxygen absorption regions. Within the absorption features, SIF contribution on satellite-derived surface apparent reflectance generates a characteristic peaky spectrum. However, the shape of these peaks can be simultaneously distorted through the atmospheric correction process due to inaccuracies in the aerosol characterization among other secondary sources. Inaccuracies in the estimation of aerosol optical thickness, Angstrom exponent, asymmetry of the scattering or single scattering albedo translate into characteristic distortions in the shape of the peaks in the apparent reflectance. This particular behaviour allows inferring the magnitude of the errors and correcting them. The presented technique improves the accuracy of any a priori aerosol retrieval.</p><p>Authors expect this study to be also of interest to other hyperspectral missions when exploiting, at high spectral resolution, information from oxygen absorption regions.</p>

scholarly journals IMK/IAA MIPAS temperature retrieval version 8: nominal measurements

2020 ◽  
Author(s):  
Michael Kiefer ◽  
Thomas von Clarmann ◽  
Bernd Funke ◽  
Maya García-Comas ◽  
Norbert Glatthor ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Spectral Resolution ◽  
Spectroscopic Data ◽  
A Priori ◽  
Michelson Interferometer ◽  
High Spectral Resolution ◽  
Transfer Model ◽  
Random Component ◽  
Horizontal Structure ◽  
Total Uncertainty

Abstract. A new global set of atmospheric temperature profiles is retrieved from recalibrated radiance spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Changes with respect to previous data versions include a new radiometric calibration considering the time-dependency of the detector non-linearity, and a more robust frequency calibration scheme. Temperature is retrieved using a smoothing constraint, while tangent altitude pointing information is constrained using optimal estimation. ECMWF ERA-Interim is used as temperature a priori below 43 km. Above, a priori data is based on data from the Whole Atmosphere Community Climate Model Version 4 (WACCM4). Bias-corrected fields from specified dynamics runs, sampled at the MIPAS times and locations, are used, blended with ERA-Interim between 43 and 53 km. Horizontal variability of temperature is considered by scaling an a priori 3D temperature field in the orbit plane in a way that the horizontal structure is provided by the a priori while the vertical structure comes from the measurements. Additional microwindows with better sensitivity at higher altitudes are used. The background continuum is jointly fitted with the target parameters up to 58 km altitude. The radiance offset correction is strongly regularized towards an empirically determined vertical offset profile. In order to avoid the propagation of uncertainties of O3 and H2O a priori assumptions, the abundances of these species are retrieved jointly with temperature. The retrieval is based on HITRAN 2016 spectroscopic data, with a few amendments. Temperature-adjusted climatologies of vibrational populations of CO2 states emitting in the 15 micron region are used in the radiative transfer modelling in order to account for non-local thermodynamic equilibrium. Numerical integration in the radiative transfer model is now performed at higher accuracy. The random component of the temperature uncertainty typically varies between 0.4 and 0.8 K, with occasional excursions up to 1.3 K above 60 km altitude. The leading sources of the random component of the temperature error are measurement noise, gain calibration uncertainty, spectral shift, and uncertain CO2 mixing ratios. The systematic error is caused by uncertainties in spectroscopic data and line shape uncertainties. It ranges from 0.2 K at 24 km altitude for northern midlatitude nighttime conditions to 2.3 K at 12 km for tropical nighttime conditions. The estimated total uncertainty amounts to values between 0.5 K at 24 km and northern polar winter conditions to 2.3 K at 12 km and northern midlatitude day conditions. The vertical resolution varies around 3 km for altitudes below 50 km. The long-term drift encountered in the previous temperature product has been largely reduced. The consistency between high spectral resolution results from 2002–2004 and the reduced spectral resolution results from 2005–2012 has been largely improved. As expected, most pronounced temperature differences between version 8 and previous data versions are found in elevated stratopause situations. The fact that the phase of temperature waves seen by MIPAS is not locked to the wave phase found in ECMWF analyses demonstrates that our retrieval provides independent information and does not merely reproduce the prior information.

scholarly journals High-Resolution Fourier Transform Spectroscopy with a VLT

1984 ◽  
Vol 79 ◽  
pp. 497-497
Author(s):  
Donald N.B. Hall
Keyword(s):  
Fourier Transform ◽  
High Resolution ◽  
Spectral Resolution ◽  
Thermal Infrared ◽  
The Other ◽  
High Spectral Resolution ◽  
Resolution Element ◽  
Infrared Wavelengths ◽  
Frequency Calibration ◽  
Absorption Features

The major advantages of the FTS technique are (1) multiplexing, (2) throughput, (3) instrumental profile, (4) stability of frequency calibration, and (5) spectrophotometry accuracy. The multiplex advantage is realized only if one is detector noise limited for the signal within an individual spectral-resolution element. At optical and thermal infrared wavelengths, this is only the case at high spectral resolution (≥ 50000) for modern detectors. By the time the VLT is operating one expects this to also be the case in the 1- to 2.5-micron region. At resolutions ≥ 50000 there are severe problems matching dispersive spectrographs to the VLT aperture, whereas existing FTS instruments already have adequate through-put to match to fields of a few arcsec with a VLT. When the other advantages are considered, the FTS is the instrument of choice for high-resolution (≥ 50000) spectroscopy of absorption features with a VLT. Foreseeable astrophysical applications include observations of interstellar and circumstellar features and of fully resolved profiles of photospheric and planetary lines.

scholarly journals Compensation of Oxygen Transmittance Effects for Proximal Sensing Retrieval of Canopy–Leaving Sun–Induced Chlorophyll Fluorescence

2018 ◽  
Vol 10 (10) ◽  
pp. 1551 ◽  
Author(s):  
Neus Sabater ◽  
Jorge Vicent ◽  
Luis Alonso ◽  
Jochem Verrelst ◽  
Elizabeth Middleton ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Spectral Resolution ◽  
Transfer Functions ◽  
Spectral Response ◽  
High Spectral Resolution ◽  
Transfer Model ◽  
Atmospheric Effects ◽  
Proximal Sensing ◽  
Field Station ◽  
Absorption Features

Estimates of Sun–Induced vegetation chlorophyll Fluorescence (SIF) using remote sensing techniques are commonly determined by exploiting solar and/or telluric absorption features. When SIF is retrieved in the strong oxygen (O 2 ) absorption features, atmospheric effects must always be compensated. Whereas correction of atmospheric effects is a standard airborne or satellite data processing step, there is no consensus regarding whether it is required for SIF proximal–sensing measurements nor what is the best strategy to be followed. Thus, by using simulated data, this work provides a comprehensive analysis about how atmospheric effects impact SIF estimations on proximal sensing, regarding: (1) the sensor height above the vegetated canopy; (2) the SIF retrieval technique used, e.g., Fraunhofer Line Discriminator (FLD) family or Spectral Fitting Methods (SFM); and (3) the instrument’s spectral resolution. We demonstrate that for proximal–sensing scenarios compensating for atmospheric effects by simply introducing the O 2 transmittance function into the FLD or SFM formulations improves SIF estimations. However, these simplistic corrections still lead to inaccurate SIF estimations due to the multiplication of spectrally convolved atmospheric transfer functions with absorption features. Consequently, a more rigorous oxygen compensation strategy is proposed and assessed by following a classic airborne atmospheric correction scheme adapted to proximal sensing. This approach allows compensating for the O 2 absorption effects and, at the same time, convolving the high spectral resolution data according to the corresponding Instrumental Spectral Response Function (ISRF) through the use of an atmospheric radiative transfer model. Finally, due to the key role of O 2 absorption on the evaluated proximal–sensing SIF retrieval strategies, its dependency on surface pressure (p) and air temperature (T) was also assessed. As an example, we combined simulated spectral data with p and T measurements obtained for a one–year period in the Hyytiälä Forestry Field Station in Finland. Of importance hereby is that seasonal dynamics in terms of T and p, if not appropriately considered as part of the retrieval strategy, can result in erroneous SIF seasonal trends that mimic those of known dynamics for temperature–dependent physiological responses of vegetation.

scholarly journals Long-term validation of ESA operational retrieval (version 6.0) of MIPAS Envisat vertical profiles of methane, nitrous oxide, CFC11, and CFC12 using balloon-borne observations and trajectory matching

2016 ◽  
Vol 9 (3) ◽  
pp. 1051-1062 ◽  
Author(s):  
Andreas Engel ◽  
Harald Bönisch ◽  
Tim Schwarzenberger ◽  
Hans-Peter Haase ◽  
Katja Grunow ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
European Space Agency ◽  
High Spectral Resolution ◽  
Vertical Profiles ◽  
Validation Data ◽  
Data Set ◽  
Mixing Ratios ◽  
Trajectory Matching ◽  
Wide Range ◽  
Resolution Data

Abstract. MIPAS-Envisat is a satellite-borne sensor which measured vertical profiles of a wide range of trace gases from 2002 to 2012 using IR emission spectroscopy. We present geophysical validation of the MIPAS-Envisat operational retrieval (version 6.0) of N2O, CH4, CFC-12, and CFC-11 by the European Space Agency (ESA). The geophysical validation data are derived from measurements of samples collected by a cryogenic whole air sampler flown to altitudes of up to 34 km by means of large scientific balloons. In order to increase the number of coincidences between the satellite and the balloon observations, we applied a trajectory matching technique. The results are presented for different time periods due to a change in the spectroscopic resolution of MIPAS in early 2005. Retrieval results for N2O, CH4, and CFC-12 show partly good agreement for some altitude regions, which differs for the periods with different spectroscopic resolution. The more recent low spectroscopic resolution data above 20 km altitude show agreement with the combined uncertainties, while there is a tendency of the earlier high spectral resolution data set to underestimate these species above 25 km. The earlier high spectral resolution data show a significant overestimation of the mixing ratios for N2O, CH4, and CFC-12 below 20 km. These differences need to be considered when using these data. The CFC-11 results from the operation retrieval version 6.0 cannot be recommended for scientific studies due to a systematic overestimation of the CFC-11 mixing ratios at all altitudes.

scholarly journals Note on rotational-Raman scattering in the O<sub>2</sub> A- and B-bands: implications for retrieval of trace-gas concentrations and terrestrial chlorophyll fluorescence

2012 ◽  
Vol 5 (6) ◽  
pp. 8789-8813 ◽  
Author(s):  
A. Vasilkov ◽  
J. Joiner ◽  
R. Spurr
Keyword(s):  
Chlorophyll Fluorescence ◽  
Raman Scattering ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Trace Gas ◽  
Absorption Bands ◽  
Spectral Signatures ◽  
The Impact ◽  
Compare And Contrast ◽  
Aerosol Characterization

Abstract. Quantifying the impact of rotational Raman scattering (RRS) on the O2 A- and B-bands is important as these bands can be used for cloud- and aerosol-characterization for trace-gas retrievals including CO2 and CH4. In this paper, we simulate the spectral effects of RRS for various viewing geometries and instruments with different spectral resolutions. We also examine how aerosols affect the amount of RRS filling-in. We show that the filling-in effects of RRS are relatively small, but not negligible, in these O2 absorption bands, particularly for high spectral resolution instruments. For comparison, we also compare and contrast the spectral signatures of RRS with those of terrestrial chlorophyll fluorescence.

scholarly journals Multiple scattering effects on the return spectrum of oceanic high-spectral-resolution lidar

2019 ◽  
Vol 27 (21) ◽  
pp. 30204
Author(s):  
Yudi Zhou ◽  
Weibiao Chen ◽  
Dong Liu ◽  
Xiaoyu Cui ◽  
Xiaolei Zhu ◽  
...  
Keyword(s):  
Multiple Scattering ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Scattering Effects ◽  
High Spectral Resolution Lidar ◽  
Multiple Scattering Effects

scholarly journals Note on rotational-Raman scattering in the O<sub>2</sub> A- and B-bands

2013 ◽  
Vol 6 (4) ◽  
pp. 981-990 ◽  
Author(s):  
A. Vasilkov ◽  
J. Joiner ◽  
R. Spurr
Keyword(s):  
Chlorophyll Fluorescence ◽  
Raman Scattering ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Trace Gas ◽  
Absorption Bands ◽  
Spectral Signatures ◽  
The Impact ◽  
Compare And Contrast ◽  
Aerosol Characterization

Abstract. Quantifying the impact of rotational-Raman scattering (RRS) on the O2 A- and B-bands is important as these bands can be used for cloud and aerosol characterization for trace-gas retrievals including CO2 and CH4. In this paper, we simulate the spectral effects of RRS for various viewing geometries and instruments with different spectral resolutions. We also examine how aerosols affect the amount of RRS filling-in. We show that the filling-in effects of RRS are relatively small, but not negligible, in these O2 absorption bands, particularly for high-spectral-resolution instruments. For comparison, we also compare and contrast the spectral signatures of RRS with those of terrestrial chlorophyll fluorescence.

scholarly journals Towards Developing a Micropulse Differential Absorption Lidar to Measure Atmospheric Temperature

2020 ◽  
Vol 237 ◽  
pp. 06018
Author(s):  
Robert A. Stillwell ◽  
Scott M. Spuler ◽  
Matthew Hayman ◽  
Catharine E. Bunn ◽  
Kevin S. Repasky
Keyword(s):  
Spectral Resolution ◽  
Atmospheric Temperature ◽  
High Spectral Resolution ◽  
Direct Result ◽  
Oxygen Absorption ◽  
Doppler Broadening ◽  
Differential Absorption ◽  
Differential Absorption Lidar ◽  
Retrieval Method ◽  
Aerosol Parameters

It has generally been assumed that differential absorption lidar (DIAL) systems are incapable of measuring atmospheric temperature with useful accuracy. This assumption is a direct result of errors that arise in standard DIAL retrievals due to differential Rayleigh-Doppler broadening from aerosols and molecules. We present here, a combined high spectral resolution (HSRL) and DIAL system that addresses this identified source of uncertainty by measuring quantitative aerosol parameters as well as oxygen absorption parameters. This system, in combination with a perturbative retrieval method, accounts for the Rayleigh-Doppler broadening effects on the oxygen absorption. We describe this combined DIAL/HSRL system and retrieval to evaluate the first retrieval parameters exploring the likelihood that it is possible to measure atmospheric temperature using a DIAL system.

scholarly journals NASA LaRC airborne high spectral resolution lidar aerosol measurements during MILAGRO: observations and validation

2009 ◽  
Vol 9 (2) ◽  
pp. 8817-8856 ◽  
Author(s):  
R. R. Rogers ◽  
J. W. Hair ◽  
C. A. Hostetler ◽  
R. A. Ferrare ◽  
M. D. Obland ◽  
...  
Keyword(s):  
Optical Depth ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Aerosol Extinction ◽  
Current State ◽  
Aerosol Scattering ◽  
Visible Wavelengths ◽  
Langley Research Center ◽  
High Spectral Resolution Lidar ◽  
532 Nm

Abstract. The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) measures vertical profiles of aerosol extinction, backscatter, and depolarization at both 532 nm and 1064 nm. In March of 2006 the HSRL participated in the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign along with several other suites of instruments deployed on both aircraft and ground based platforms. This paper presents high spatial and vertical resolution HSRL measurements of aerosol extinction and optical depth from MILAGRO and comparisons of those measurements with similar measurements from other sensors and model predictions. HSRL measurements coincident with airborne in situ aerosol scattering and absorption measurements from two different instrument suites on the C-130 and G-1 aircraft, airborne aerosol optical depth (AOD) and extinction measurements from an airborne tracking sunphotometer on the J-31 aircraft, and AOD from a network of ground based Aerosol Robotic Network (AERONET) sun photometers are presented as a validation of the HSRL aerosol extinction and optical depth products. Regarding the extinction validation, we find bias differences between HSRL and these instruments to be less than 3% (0.01 km−1) at 532 nm, the wavelength at which the HSRL technique is employed. The rms differences at 532 nm were less than 50% (0.015 km−1). To our knowledge this is the most comprehensive validation of the HSRL measurement of aerosol extinction and optical depth to date. The observed bias differences in ambient aerosol extinction between HSRL and other measurements is within 15–20% at visible wavelengths, found by previous studies to be the differences observed with current state-of-the-art instrumentation (Schmid et al., 2006).

scholarly journals NASA LaRC airborne high spectral resolution lidar aerosol measurements during MILAGRO: observations and validation

2009 ◽  
Vol 9 (14) ◽  
pp. 4811-4826 ◽  
Author(s):  
R. R. Rogers ◽  
J. W. Hair ◽  
C. A. Hostetler ◽  
R. A. Ferrare ◽  
M. D. Obland ◽  
...  
Keyword(s):  
Optical Depth ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Aerosol Extinction ◽  
Current State ◽  
Aerosol Scattering ◽  
Visible Wavelengths ◽  
Langley Research Center ◽  
High Spectral Resolution Lidar ◽  
532 Nm

Abstract. The NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) measures vertical profiles of aerosol extinction, backscatter, and depolarization at both 532 nm and 1064 nm. In March of 2006 the HSRL participated in the Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign along with several other suites of instruments deployed on both aircraft and ground based platforms. This paper presents high spatial and vertical resolution HSRL measurements of aerosol extinction and optical depth from MILAGRO and comparisons of those measurements with similar measurements from other sensors and model predictions. HSRL measurements coincident with airborne in situ aerosol scattering and absorption measurements from two different instrument suites on the C-130 and G-1 aircraft, airborne aerosol optical depth (AOD) and extinction measurements from an airborne tracking sunphotometer on the J-31 aircraft, and AOD from a network of ground based Aerosol Robotic Network (AERONET) sun photometers are presented as a validation of the HSRL aerosol extinction and optical depth products. Regarding the extinction validation, we find bias differences between HSRL and these instruments to be less than 3% (0.01 km−1) at 532 nm, the wavelength at which the HSRL technique is employed. The rms differences at 532 nm were less than 50% (0.015 km−1). To our knowledge this is the most comprehensive validation of the HSRL measurement of aerosol extinction and optical depth to date. The observed bias differences in ambient aerosol extinction between HSRL and other measurements is within 15–20% at visible wavelengths, found by previous studies to be the differences observed with current state-of-the-art instrumentation (Schmid et al., 2006).

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