The Tropospheric Monitoring Instrument (TROPOMI) is the single instrument on board the ESA Copernicus Sentinel-5 Precursor satellite. TROPOMI is a nadir-viewing imaging spectrometer with bands in the ...ultraviolet and visible, the near infrared and the shortwave infrared (SWIR). An accurate instrument spectral response function (ISRF) is required in the SWIR band where absorption lines of CO, methane and water vapor overlap. In this paper, we report on the determination of the TROPOMI-SWIR ISRF during an extensive on-ground calibration campaign. Measurements are taken with a monochromatic light source scanning the whole detector, using the spectrometer itself to determine the light intensity and wavelength. The accuracy of the resulting ISRF calibration key data is well within the requirement for trace-gas retrievals. Long-term in-flight monitoring of SWIR ISRF is achieved using five on-board diode lasers.
Southeast Australia experienced intensive and geographically extensive wildfires during the 2019-2020 summer season. The fires released substantial amounts of carbon dioxide into the atmosphere. ...However, existing emission estimates based on fire inventories are uncertain, and vary by up to a factor of four for this event. Here we constrain emission estimates with the help of satellite observations of carbon monoxide, an analytical Bayesian inversion and observed ratios between emitted carbon dioxide and carbon monoxide. We estimate emissions of carbon dioxide to be 715 teragrams (range 517-867) from November 2019 to January 2020. This is more than twice the estimate derived by five different fire inventories, and broadly consistent with estimates based on a bottom-up bootstrap analysis ofthis fire episode. Although fires occur regularly in the savannas in northern Australia, the recent episodes were extremely large in scale and intensity, burning unusually large areas of eucalyptus forest in the southeast. The fires were driven partly by climate change, making better-constrained emission estimates particularly important. This is because the build-up of atmospheric carbon dioxide may become increasingly dependent on fire-driven climate-carbon feedbacks, as highlighted by this event.
Methane emissions due to accidents in the oil and natural gas sector are very challenging to monitor, and hence are seldom considered in emission inventories and reporting. One of the main reasons is ...the lack of measurements during such events. Here we report the detection of large methane emissions from a gas well blowout in Ohio during February to March 2018 in the total column methane measurements from the spaceborne Tropospheric Monitoring Instrument (TROPOMI). From these data, we derive a methane emission rate of 120 ± 32 metric tons per hour. This hourly emission rate is twice that of the widely reported Aliso Canyon event in California in 2015. Assuming the detected emission represents the average rate for the 20-d blowout period, we find the total methane emission from the well blowout is comparable to one-quarter of the entire state of Ohio’s reported annual oil and natural gas methane emission, or, alternatively, a substantial fraction of the annual anthropogenic methane emissions from several European countries. Our work demonstrates the strength and effectiveness of routine satellite measurements in detecting and quantifying greenhouse gas emission from unpredictable events. In this specific case, the magnitude of a relatively unknown yet extremely large accidental leakage was revealed using measurements of TROPOMI in its routine global survey, providing quantitative assessment of associated methane emissions.
We are developing a kilo-pixels Ti/Au TES array as a backup option for Athena X-IFU. Here we report on single-pixel performance of a 32 × 32 array operated in a Frequency Division Multiplexing (FDM) ...readout system, with bias frequencies in the range 1-5 MHz. We have tested the pixels response at several photon energies, by means of a <inline-formula><tex-math notation="LaTeX">^{55}</tex-math></inline-formula>Fe radioactive source (emitting Mn-K<inline-formula><tex-math notation="LaTeX">\alpha</tex-math></inline-formula> at 5.9 keV) and a Modulated X-ray Source (MXS, providing Cr-K<inline-formula><tex-math notation="LaTeX">\alpha</tex-math></inline-formula> at 5.4 keV and Cu-K<inline-formula><tex-math notation="LaTeX">\alpha</tex-math></inline-formula> at 8.0 keV). First, we report the procedure used to perform the detector energy scale calibration, usually achieving a calibration accuracy better than <inline-formula><tex-math notation="LaTeX">\sim</tex-math></inline-formula>0.5 eV in the 5.4-8.9 keV energy range. Then, we present the measured energy resolution at the different energies (best single pixel performance: <inline-formula><tex-math notation="LaTeX">\Delta</tex-math></inline-formula> E <inline-formula><tex-math notation="LaTeX">_{\mathrm{FWHM}}</tex-math></inline-formula> = 2.40 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.09 eV @ 5.4 keV; 2.53 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.10 eV @ 5.9 keV; 2.78 <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.16 eV @ 8.0 keV), investigating also the performance dependency from the pixel bias frequency and the count rate. Thanks to long background measurements (<inline-formula><tex-math notation="LaTeX">\sim</tex-math></inline-formula>1 d), we finally detected also the Al-K<inline-formula><tex-math notation="LaTeX">\alpha</tex-math></inline-formula> line at 1.5 keV, generated by fluorescence inside the experimental setup. We analyzed this line to obtain a first assessment of the single-pixel performance also at low energy (<inline-formula><tex-math notation="LaTeX">\Delta</tex-math></inline-formula> E <inline-formula><tex-math notation="LaTeX">_{\mathrm{FWHM}}</tex-math></inline-formula> = 1.91 eV <inline-formula><tex-math notation="LaTeX">\pm</tex-math></inline-formula> 0.21 eV @ 1.5 keV), and to evaluate the linearity of the detector response in a large energy band (1.5-8.9 keV).
The shortwave infrared (SWIR) spectrometer module of the Tropospheric
Monitoring Instrument (TROPOMI), on board the ESA Copernicus Sentinel-5
Precursor satellite, is used to measure atmospheric CO ...and methane columns.
For this purpose, calibrated radiance measurements are needed that are
minimally contaminated by instrumental stray light. Therefore, a method has
been developed and applied in an on-ground calibration campaign to
characterize stray light in detail using a monochromatic quasi-point light
source. The dynamic range of the signal was extended to more than 7 orders of magnitude by performing measurements with different exposure times,
saturating detector pixels at the longer exposure times. Analysis of the
stray light indicates about 4.4 % of the detected light is correctable stray
light. An algorithm was then devised and implemented in the operational data
processor to correct in-flight SWIR observations in near-real time, based on
Van Cittert deconvolution. The stray light is approximated by a far-field
kernel independent of position and wavelength and an additional kernel
representing the main reflection. Applying this correction significantly
reduces the stray-light signal, for example in a simulated dark forest scene
close to bright clouds by a factor of about 10. Simulations indicate that
this reduces the stray-light error sufficiently for accurate gas-column
retrievals. In addition, the instrument contains five SWIR diode lasers that
enable long-term, in-flight monitoring of the stray-light distribution.
Space qualified InGaAs solid-state array detectors, covering the near-infrared 1–2.4 μm wavelength range, have been developed for application in space-based spectroscopy of the Earth atmosphere. The ...SCIAMACHY atmospheric chemistry instrument on the ESA ENVISAT satellite (2002–2005) will be equipped with a series of these novel detectors. Detectors are arranged in linear arrays of 1024 pixels of 25×500 μm
2 dimension and meet requirements on modestly low operating temperature (150 K) and low levels of dark current and noise. In this paper the underlying physics of dark current and noise of the detector system is studied on the basis of a theoretical model in combination with measurements. At 2.4 μm wavelength the dark-current performance achieved is 20–100 fA at an operating temperature of 150 K and a bias voltage of −2 mV. This corresponds to a figure of merit for detector resistance
R
0 times detector pixel area
A of
R
0
A=2.5–12.5 MΩ
cm
2. This result has required the development of a customised multiplexer for parallel detector read-out at near-zero bias voltage. Further reduction of the operating temperature will not result in lowering the dark current and noise of the InGaAs detectors which are shown to be limited by tunnelling current. A route to future improvement is discussed.
A Superconducting Integrated Receiver (SIR) was proposed more than 10 years ago and has since then been developed up to the point of practical applications. We have demonstrated for the first time ...the capabilities of the SIR technology for heterodyne spectroscopy both in the laboratory and at remote operation under harsh environmental conditions for atmospheric research. Within a SIR the main components needed for a superconducting heterodyne receiver such as an SIS-mixer with quasi-optical antenna, a Flux-Flow oscillator (FFO) as the local oscillator, and a harmonic mixer to phase-lock the FFO are integrated on a single chip. Light weight and low power consumption combined with broadband operation and nearly quantum limited sensitivity make the SIR a perfect candidate for future airborne and space-borne missions. The noise temperature of the SIR was measured to be as low as 85 K, with an intermediate frequency band of 4-8 GHz in double sideband operation; the spectral resolution is well below 1 MHz. The SIR was implemented in the three-channel balloon-borne instrument TELIS (TErahertz and submillimeter LImb Sounder) that detects spectral emission lines of stratospheric trace gases (like ClO and BrO). These gases even in small quantities can have a significant impact on the atmosphere because they speed up certain chemical processes, such as ozone depletion.
In this report an overview of the results on the development of a single-chip superconducting integrated receiver for the Terahertz Limb Sounder (TELIS) balloon project intended to measure a variety ...of stratosphere trace gases is presented. The Superconducting Integrated Receiver (SIR) comprises in one chip a planar antenna integrated with a superconductor-insulator-superconductor (SIS) mixer, a superconducting Flux Flow Oscillator (FFO) acting as local oscillator (LO) and a second SIS harmonic mixer (HM) for FFO phase locking. As a result of the FFO design optimization a free-running linewidth between 9 and 1.5 MHz has been measured in the frequency range 500-710 GHz resulting in phase-locking of 35 to 95% of the FFO power correspondingly. A new generation of the SIR devices with improved FFO performance and optimized interface between FFO and SIS/HM has been developed and comprehensively tested. As a result all required TELIS parameters were demonstrated. Phase-locked FFO operation over entire SIR channel frequency range has been realized, spectral resolution below 1 MHz has been confirmed by gas cell and CW signal measurements. An uncorrected double side band (DSB) noise temperature below 250 K has been measured with the phase-locked FFO. The intermediate frequency bandwidth 4-8 GHz has been realized. To ensure remote operation of the phase-locked SIR several procedures for its automatic computer control have been developed and tested.
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