Determination of the TROPOMI-SWIR instrument spectral response function

Hees, Richard M. van; Tol, Paul; Cadot, Sidney; Krijger, Matthijs; Persijn, Stefan; Kempen, T. A. van; Snel, Ralph; Aben, I.; Hoogeveen, Ruud W. M.

doi:10.5194/amt-11-3917-2018

Cited by 23 publications

(23 citation statements)

References 11 publications

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“…Each diffuser can be employed in oscillation mode to suppress speckles observed in the laser signal. Due a limited operational lifetime and excess heat produced by the oscillating diffuser, it was decided to not oscillate the diffuser during nominal operations (van Hees et al, 2018). Table 1 lists the parameters for which calibration parameters, the CKD, or monitoring data are derived.…”

Section: Calibration Planmentioning

confidence: 99%

In-flight calibration and monitoring of the TROPOMI-SWIR module

Kempen

Hees

Tol

et al. 2019

Preprint

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Abstract. During its first year in operation the SWIR module of the TROPOMI instrument was calibrated in-flight and its performance was monitored. In this paper we present the results of the in-flight calibration and the ongoing instrument monitoring. This includes the determination of the background signals, noise performance, ISRF stability and stray-light stability. From these results, the number of incurred dead and bad pixels due to cosmic-ray impacts is determined. The light-path transmission is checked by monitoring internal lamp and diffuser stabilities. Due to its high sensitivity for Earth radiation on the eclips side, the calibration strategy for the background (i.e. dark flux and offset) monitoring was adjusted. Trends over the first full year of nominal operations reveal a very stable SWIR module with little to no degradation. The number of newly incurred dead and bad pixels is negligible since the start of operations. Assuming linear degradation of various component, the SWIR module is expected to keep performing within expected parameters for the full operational lifetime.

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Section: Calibration Planmentioning

confidence: 99%

In-flight calibration and monitoring of the TROPOMI-SWIR module

Kempen

Hees

Tol

et al. 2019

Preprint

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“…The OMI ISRFs have been parameterized as a standard Gaussian from climatological OMI solar irradiances for each UV1 and UV2 band and thereby these PAs could take into account the spectral fitting responses caused by temporal variations in the slit function. This ozone fitting procedure uses ISRFs to convolve high-resolution absorption spectra, taken from Brion et al (1993) for ozone ab-sorption cross sections and Wilmouth et al (1999) for BrO absorption cross sections. In DOAS analysis, the pseudo absorber is defined as ∂S ∂p ⊗ σ h (σ h is a high-resolution absorption cross section), which could be calculated at a computationally low cost.…”

Section: Implementation Of the Slit Function Linearization In The Saomentioning

confidence: 99%

Linearization of the effect of slit function changes for improving Ozone Monitoring Instrument ozone profile retrievals

et al. 2019

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Abstract. We introduce a method that accounts for errors caused by the slit function in an optimal-estimation-based spectral fitting process to improve ozone profile retrievals from the Ozone Monitoring Instrument (OMI) ultraviolet measurements (270–330 nm). Previously, a slit function was parameterized as a standard Gaussian by fitting the full width at half maximum (FWHM) of the slit function from climatological OMI solar irradiances. This cannot account for the temporal variation in slit function in irradiance, the intra-orbit changes due to thermally induced change and scene inhomogeneity, and potential differences in the slit functions of irradiance and radiance measurements. As a result, radiance simulation errors may be induced due to convolving reference spectra with incorrect slit functions. To better represent the shape of the slit functions, we implement a more generic super Gaussian slit function with two free parameters (slit width and shape factor); it becomes standard Gaussian when the shape factor is fixed to be 2. The effects of errors in slit function parameters on radiance spectra, referred to as pseudo absorbers (PAs), are linearized by convolving high-resolution cross sections or simulated radiances with the partial derivatives of the slit function with respect to the slit parameters. The PAs are included in the spectral fitting scaled by fitting coefficients that are iteratively adjusted as elements of the state vector along with ozone and other fitting parameters. The fitting coefficients vary with cross-track and along-track pixels and show sensitivity to heterogeneous scenes. The PA spectrum is quite similar in the Hartley band below 310 nm for both standard and super Gaussians, but is more distinctly structured in the Huggins band above 310 nm with the use of super Gaussian slit functions. Finally, we demonstrate that some spikes of fitting residuals are slightly smoothed by accounting for the slit function errors. Comparisons with ozonesondes demonstrate noticeable improvements when using PAs for both standard and super Gaussians, especially for reducing the systematic biases in the tropics and midlatitudes (mean biases of tropospheric column ozone reduced from -1.4∼0.7 to 0.0∼0.4 DU) and reducing the standard deviations of tropospheric ozone column differences at high latitudes (by 1 DU for the super Gaussian). Including PAs also makes the retrievals consistent between standard and super Gaussians. This study corroborates the slit function differences between radiance and irradiance, demonstrating that it is important to account for such differences in the ozone profile retrievals.

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“…For space-borne instruments, ISRFs are typically characterized as a function of the detector dimensions using a tunable laser source prior to the launch (Dirksen et al, 2006;Liu et al, 2015;van Hees et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Linearization of the effect of slit function changes for improving OMI ozone profile retrievals

Bak

Liu

Sun

et al. 2019

Preprint

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Abstract. We introduce a method that reduces the spectral fit residuals caused by the slit function errors in an optimal estimation based spectral fitting process to improve ozone profile retrievals from the Ozone Monitoring Instrument (OMI) ultraviolet measurements (270–330 nm). Previously, a slit function was parameterized as a standard Gaussian by fitting the Full Width at Half Maximum (FWHM) of the slit function from climatological OMI solar irradiances. This cannot account for the temporal variation of slit function in irradiance, the intra-orbit slit function changes due to thermally-induced change and scene inhomogeneity, and potential differences in the slit functions of irradiance and radiance measurements. As a result, radiance simulation errors may be induced due to using the convolved reference spectra with incorrect slit functions. To better represent the shape of the slit functions, we implement a more generic super Gaussian slit function with two free parameters (slit width and shape factor); it becomes standard Gaussian when the shape factor is fixed to be 2. The effects of errors in slit function parameters on radiance spectra, referred as Pseudo Absorbers (PAs), are linearized by convolving high-resolution cross sections or simulated radiances with the partial derivatives of the slit function with respect to the slit parameters. The PAs are included in the spectral fitting scaled by fitting coefficients that are iteratively adjusted as elements of the state vector along with ozone and other fitting parameters. The fit coefficients vary with cross-track and along-track pixels and show sensitivity to heterogeneous scenes. The total PA spectrum is quite similar in the Hartley band below 310 nm for both standard and super Gaussians, but is more distinctly structured in the Huggins band above 310 nm with the use of super Gaussian slit functions. Finally, we demonstrate that some spikes of fitting residuals are slightly smoothed by accounting for the slit function errors. Comparisons with ozonesondes demonstrate substantial improvements with the use of PAs for both standard and super Gaussians, especially for reducing the systematic biases in the tropics and mid-latitudes and reducing the standard deviations at high-latitudes. Including PAs also makes the retrievals consistent between standard and super Gaussians. This study corroborates the slit function differences between radiance and irradiance demonstrating that it is important to account for such differences in the ozone profile retrievals.

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Determination of the TROPOMI-SWIR instrument spectral response function

Cited by 23 publications

References 11 publications

In-flight calibration and monitoring of the TROPOMI-SWIR module

In-flight calibration and monitoring of the TROPOMI-SWIR module

Linearization of the effect of slit function changes for improving Ozone Monitoring Instrument ozone profile retrievals

Linearization of the effect of slit function changes for improving OMI ozone profile retrievals

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