103 research outputs found
Global Retrievals of Solar-Induced Chlorophyll Fluorescence With TROPOMI: First Results and Intersensor Comparison to OCO-2
In recent years, solarâinduced chlorophyll fluorescence (SIF) retrieved from spaceborne spectrometers has been extensively used as a proxy for terrestrial photosynthesis at relatively sparse temporal and spatial scales. The nearâinfrared band of the recently launched TROPOspheric Monitoring Instrument (TROPOMI) features the required spectral resolution and signalâtoânoise ratio to retrieve SIF in a spectral range devoid of atmospheric absorption features. We find that initial TROPOMI spectra meet high expectations for a substantially improved spatiotemporal resolution (up to 7âkm Ă 3.5âkm pixels with daily revisit), representing a step change in SIF remote sensing capabilities. However, interpretation requires caution, as the broad range of viewingâillumination geometries covered by TROPOMI's 2,600âkmâwide swath needs to be taken into account. A first intersensor comparison with OCOâ2 (Orbiting Carbon Observatoryâ2) SIF shows excellent agreement, underscoring the high quality of TROPOMI's SIF retrievals and the notable radiometric performance of the instrument
Global Retrievals of Solar-Induced Chlorophyll Fluorescence at Red Wavelengths With TROPOMI
Observations of solarâinduced chlorophyll a fluorescence (SIF) from spaceborne spectrometers can advance our understanding of terrestrial and aquatic carbon cycles. Here we present the first global retrievals of SIF at red wavelengths from the TROPOspheric Monitoring Instrument (TROPOMI). Despite the weak signal level, considerable uncertainties, and subtle measurement artifacts, spatial patterns and magnitudes agree with independent data sets. Over land, spatial patterns of our red SIF estimates covary with the farâred SIF data. Red SIF over the ocean is highly consistent with the normalized fluorescence line height (nFLH) inferred from measurements of the MODerate resolution Imaging Spectroradiometer (MODIS), even when comparing single days and fine spatial scales. Major advantages of our Fraunhofer lineâbased SIF retrievals include the capability to sense SIF through optically thin cloud/aerosol layers and an insensitivity to ocean color. This opens up new avenues for studying ocean biogeochemistry from space
Techniques for Galactic Dust Measurements in the Heliosphere
Galactic interstellar dust (ISD) is the major ingredient in planetary
formation. However, information on this important material has been extremely
limited. Recently the Ulysses dust detector has identified and measured
interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above
. Inside this distance it could not reliably distinguish
interstellar from interplanetary dust. Modeling the Ulysses data suggests that
up to 30 % of dust flux with masses above at 1~AU is of
interstellar origin. From the Hiten satellite in high eccentric orbit about the
Earth there are indications that ISD indeed reaches the Earth's orbit. Two new
missions carrying dust detectors, Cassini and Stardust, will greatly increase
our observational knowledge. In this paper we briefly review instruments used
on these missions and compare their capabilities. The Stardust mission [{\em
Brownlee et al.}, 1996] will analyze the local interstellar dust population by
an in-situ chemical analyzer and collect ISD between 2 and 3~AU from the Sun.
The dust analyzer on the Cassini mission will determine the interstellar dust
flux outside Venus' orbit and will provide also some compositional information.
Techniques to identify the ISD flux levels at 1~AU are described that can
quantify the interstellar dust flux in high-Earth orbit (outside the debris
belts) and provide chemical composition information of galactic dust.Comment: Accepted for Journal of Geophysical Research, 6 figures, Late
Global Retrievals of Solar-Induced Chlorophyll Fluorescence at Red Wavelengths With TROPOMI
Observations of solarâinduced chlorophyll a fluorescence (SIF) from spaceborne spectrometers can advance our understanding of terrestrial and aquatic carbon cycles. Here we present the first global retrievals of SIF at red wavelengths from the TROPOspheric Monitoring Instrument (TROPOMI). Despite the weak signal level, considerable uncertainties, and subtle measurement artifacts, spatial patterns and magnitudes agree with independent data sets. Over land, spatial patterns of our red SIF estimates covary with the farâred SIF data. Red SIF over the ocean is highly consistent with the normalized fluorescence line height (nFLH) inferred from measurements of the MODerate resolution Imaging Spectroradiometer (MODIS), even when comparing single days and fine spatial scales. Major advantages of our Fraunhofer lineâbased SIF retrievals include the capability to sense SIF through optically thin cloud/aerosol layers and an insensitivity to ocean color. This opens up new avenues for studying ocean biogeochemistry from space
First data set of H<sub>2</sub>O/HDO columns from the Tropospheric Monitoring Instrument (TROPOMI)
Global measurements of atmospheric water vapour isotopologues aid to better understand the hydrological cycle and improve global circulation models. This paper presents a new data set of vertical column densities of H2O and HDO retrieved from short-wave infrared (2.3â”m) reflectance measurements by the Tropospheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite. TROPOMI features daily global coverage with a spatial resolution of up to 7âkmĂ7âkm. The retrieval utilises a profile-scaling approach. The forward model neglects scattering, and strict cloud filtering is therefore necessary. For validation, recent ground-based water vapour isotopologue measurements by the Total Carbon Column Observing Network (TCCON) are employed. A comparison of TCCON ÎŽD with ground-based measurements by the Multi-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water (MUSICA) project for data prior to 2014 (where MUSICA data are available) shows a bias in TCCON ÎŽD estimates. As TCCON HDO is currently not validated, an overall correction of recent TCCON HDO data is derived based on this finding. The agreement between the corrected TCCON measurements and co-located TROPOMI observations is good with an average bias of (â0.2±3)Ă10âmolecâcm ((1.1±7.2)â%) in HO and (â2±7)Ă10âmolecâcm ((â1.1±7.3)â%) in HDO, which corresponds to a mean bias of (â14±17)ââ° in a posteriori ÎŽD. The bias is lower at low- and mid-latitude stations and higher at high-latitude stations. The use of the data set is demonstrated with a case study of a blocking anticyclone in northwestern Europe in July 2018 using single-overpass data
Shipborne measurements of XCO, XCH, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses and S5P/TROPOMI
Measurements of atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2), methane (XCH4), and carbon monoxide (XCO) have been collected across the Pacific Ocean during the Measuring Ocean REferences 2 (MORE-2) campaign in June 2019. We deployed a shipborne variant of the EM27/SUN Fourier transform spectrometer (FTS) on board the German RN Sonne which, during MORE-2, crossed the Pacific Ocean from Vancouver, Canada, to Singapore. Equipped with a specially manufactured fast solar tracker, the FTS operated in direct-sun viewing geometry during the ship cruise reliably delivering solar absorption spectra in the shortwave infrared spectral range (4000 to 11000 cm(-1)). After filtering and bias correcting the dataset, we report on XCO2, XCH4, and XCO measurements for 22 d along a trajectory that largely aligns with 30 degrees N of latitude between 140 degrees W and 120 degrees E of longitude. The dataset has been scaled to the Total Carbon Column Observing Network (TCCON) station in Karlsruhe, Germany, before and after the MORE-2 campaign through side-by-side measurements. The la repeatability of hourly means of XCO2, XCH4, and XCO is found to be 0.24 ppm, 1.1 ppb, and 0.75 ppb, respectively. The Copernicus Atmosphere Monitoring Service (CAMS) models gridded concentration fields of the atmospheric composition using assimilated satellite observations, which show excellent agreement of 0.52 +/- 0.31 ppm for XCO2, 0.9 +/- 4.1 ppb for XCH4, and 3.2 +/- 3.4 ppb for XCO (mean difference +/- SD, standard deviation, of differences for entire record) with our observations. Likewise, we find excellent agreement to within 2.2 +/- 6.6 ppb with the XCO observations of the TROPOspheric MOnitoring Instrument (TROPOMI) on the Sentinel-5 Precursor satellite (S5P). The shipborne measurements are accessible at https://doi.org/10.1594/PANGAEA.917240 (Knapp et al., 2020)
Global Retrievals of Solar-Induced Chlorophyll Fluorescence With TROPOMI: First Results and Intersensor Comparison to OCO-2
In recent years, solarâinduced chlorophyll fluorescence (SIF) retrieved from spaceborne spectrometers has been extensively used as a proxy for terrestrial photosynthesis at relatively sparse temporal and spatial scales. The nearâinfrared band of the recently launched TROPOspheric Monitoring Instrument (TROPOMI) features the required spectral resolution and signalâtoânoise ratio to retrieve SIF in a spectral range devoid of atmospheric absorption features. We find that initial TROPOMI spectra meet high expectations for a substantially improved spatiotemporal resolution (up to 7âkm Ă 3.5âkm pixels with daily revisit), representing a step change in SIF remote sensing capabilities. However, interpretation requires caution, as the broad range of viewingâillumination geometries covered by TROPOMI's 2,600âkmâwide swath needs to be taken into account. A first intersensor comparison with OCOâ2 (Orbiting Carbon Observatoryâ2) SIF shows excellent agreement, underscoring the high quality of TROPOMI's SIF retrievals and the notable radiometric performance of the instrument
Intercomparison of atmospheric CO2 and CH4 abundances on regional scales in boreal areas using Copernicus Atmosphere Monitoring Service (CAMS) analysis, COllaborative Carbon Column Observing Network (COCCON) spectrometers, and Sentinel-5 Precursor satellite observations
We compare the atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO) and methane (XCH) measured with a pair of COllaborative Carbon Column Observing Network (COCCON) spectrometers at Kiruna and SodankylĂ€ (boreal areas). We compare model data provided by the Copernicus Atmosphere Monitoring Service (CAMS) between 2017 and 2019 with XCH data from the recently launched Sentinel-5 Precursor (S5P) satellite between 2018 and 2019. In addition, measured and modeled gradients of XCO and XCH (ÎXCO and ÎXCH) on regional scales are investigated. Both sites show a similar and very good correlation between COCCON retrievals and the modeled CAMS XCO data, while CAMS data are biased high with respect to COCCON by 3.72âppm (±1.80âppm) in Kiruna and 3.46âppm (±1.73âppm) in SodankylĂ€ on average. For XCH, CAMS values are higher than the COCCON observations by 0.33âppb (±11.93âppb) in Kiruna and 7.39âppb (±10.92âppb) in SodankylĂ€. In contrast, the S5P satellite generally measures lower atmospheric XCH than the COCCON spectrometers, with a mean difference of 9.69âppb (±20.51âppb) in Kiruna and 3.36âppb (±17.05âppb) in SodankylĂ€. We compare the gradients of XCO and XCH (ÎXCO and ÎXCH) between Kiruna and SodankylĂ€ derived from CAMS analysis and COCCON and S5P measurements to study the capability of detecting sources and sinks on regional scales. The correlations in ÎXCO and ÎXCH between the different datasets are generally smaller than the correlations in XCO and XCH between the datasets at either site. The ÎXCO values predicted by CAMS are generally higher than those observed with COCCON with a slope of 0.51. The ÎXCH values predicted by CAMS are mostly higher than those observed with COCCON with a slope of 0.65, covering a larger dataset than the comparison between S5P and COCCON. When comparing CAMS ÎXCH with COCCON ÎXCH only in S5P overpass days (slopeâ=â0.53), the correlation is close to that between S5P and COCCON (slopeâ=â0.51). CAMS, COCCON, and S5P predict gradients in reasonable agreement. However, the small number of observations coinciding with S5P limits our ability to verify the performance of this spaceborne sensor. We detect no significant impact of ground albedo and viewing zenith angle on the S5P results. Both sites show similar situations with the average ratios of XCH (S5P/COCCON) of 0.9949±0.0118 in Kiruna and 0.9953±0.0089 in SodankylĂ€. Overall, the results indicate that the COCCON instruments have the capability of measuring greenhouse gas (GHG) gradients on regional scales, and observations performed with the portable spectrometers can contribute to inferring sources and sinks and to validating spaceborne greenhouse gas sensors. To our knowledge, this is the first published study using COCCON spectrometers for the validation of XCH measurements collected by S5P
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