scholarly journals Evaluation and attribution of OCO-2 XCO<sub>2</sub> uncertainties

2017 ◽  
Vol 10 (7) ◽  
pp. 2759-2771 ◽  
Author(s):  
John R. Worden ◽  
Gary Doran ◽  
Susan Kulawik ◽  
Annmarie Eldering ◽  
David Crisp ◽  
...  
Keyword(s):  
Lower Bound ◽  
Carbon Cycle ◽  
Surface Albedo ◽  
Signal To Noise ◽  
Testing Hypotheses ◽  
Systematic Biases ◽  
Precision And Accuracy ◽  
Underlying Processes ◽  
Interference Error ◽  
Total Column

Abstract. Evaluating and attributing uncertainties in total column atmospheric CO2 measurements (XCO2) from the OCO-2 instrument is critical for testing hypotheses related to the underlying processes controlling XCO2 and for developing quality flags needed to choose those measurements that are usable for carbon cycle science.Here we test the reported uncertainties of version 7 OCO-2 XCO2 measurements by examining variations of the XCO2 measurements and their calculated uncertainties within small regions (∼  100 km  ×  10.5 km) in which natural CO2 variability is expected to be small relative to variations imparted by noise or interferences. Over 39 000 of these small neighborhoods comprised of approximately 190 observations per neighborhood are used for this analysis. We find that a typical ocean measurement has a precision and accuracy of 0.35 and 0.24 ppm respectively for calculated precisions larger than  ∼  0.25 ppm. These values are approximately consistent with the calculated errors of 0.33 and 0.14 ppm for the noise and interference error, assuming that the accuracy is bounded by the calculated interference error. The actual precision for ocean data becomes worse as the signal-to-noise increases or the calculated precision decreases below 0.25 ppm for reasons that are not well understood. A typical land measurement, both nadir and glint, is found to have a precision and accuracy of approximately 0.75 and 0.65 ppm respectively as compared to the calculated precision and accuracy of approximately 0.36 and 0.2 ppm. The differences in accuracy between ocean and land suggests that the accuracy of XCO2 data is likely related to interferences such as aerosols or surface albedo as they vary less over ocean than land. The accuracy as derived here is also likely a lower bound as it does not account for possible systematic biases between the regions used in this analysis.

scholarly journals Evaluation And Attribution Of OCO-2 XCO<sub>2</sub> Uncertainties

2016 ◽  
Author(s):  
John Worden ◽  
Gary Doran ◽  
Susan Kulawik ◽  
Annmarie Eldering ◽  
David Crisp ◽  
...  
Keyword(s):  
Lower Bound ◽  
Carbon Cycle ◽  
Surface Albedo ◽  
Signal To Noise ◽  
Testing Hypotheses ◽  
Synoptic Variability ◽  
Precision And Accuracy ◽  
Underlying Processes ◽  
Interference Error ◽  
Total Column

Abstract. Evaluating and attributing uncertainties in total column atmospheric CO2 measurements (XCO2) from the OCO-2 instrument is critical for testing hypotheses related to the underlying processes controlling XCO2 and for developing quality flags needed to choose those measurements that are usable for carbon cycle science. Here we test the reported uncertainties of Version 7 OCO-2 XCO2 measurements by examining variations of the XCO2 measurements and their calculated uncertainties within small regions (~ 100 km x 10.5 km) in which CO2 variability is expected to be small relative to variations imparted by noise or interferences. Over 39 000 of these “small neighborhoods” comprised of approximately 190 observations per neighborhood are used for this analysis. We find that a typical ocean measurement should have a precision and accuracy of 0.35 and 0.24 ppm respectively for calculated precisions larger than ~ 0.25 ppm. These values are approximately consistent with the calculated errors of 0.33 and 0.14 ppm for the noise and interference error (assuming that the accuracy is bounded by the calculated interference error). The actual precision for ocean data becomes worse as the signal-to-noise increases or the calculated precision decreases below 0.25 ppm for reasons that not well understood. A typical land measurement (both nadir and glint) is found to have a precision and accuracy of approximately 0.75 ppm and 0.65 ppm respectively as compared to the calculated precision and accuracy of approximately 0.36 ppm and 0.2 ppm. However, this precision includes the effects of synoptic variability in the total column that could be as high as 0.5 ppm during the summer drawdown period. The accuracy is likely related to interferences such as aerosols or surface albedo and is a lower bound as it is evaluated by comparing gradients in OCO-2 estimates of XCO2 to expected gradients across the region and not by direct comparison to well-calibrated XCO2 measurements from the ground network.

scholarly journals An SNR-Optimized Scanning Strategy for Geostationary Carbon Cycle Observatory (GeoCarb) Instrument

2018 ◽  
Author(s):  
Jeffrey Nivitanont ◽  
Sean Crowell
Keyword(s):  
Carbon Cycle ◽  
Greenhouse Gases ◽  
Optimization Problem ◽  
Signal To Noise Ratio ◽  
Western Hemisphere ◽  
Geostationary Orbit ◽  
Signal To Noise ◽  
Scanning Strategy ◽  
Land Mass ◽  
Error Distributions

Abstract. The Geostationary Carbon Observatory (GeoCarb) will make measurements of greenhouse gases over the land mass in the western hemisphere. The extreme flexibility of observing from geostationary orbit induces an optimization problem, as operators must choose what to observe and when. We express this problem in terms of an optimal subcovering problem, and use an Incremental Optimization (IO) algorithm to create a scanning strategy that minimizes expected error as a function of the signal-to-noise ratio (SNR), and show that this method outperforms the human selected strategy in terms of global error distributions.

scholarly journals Improvement of CO2-DIAL Signal-to-Noise Ratio Using Lifting Wavelet Transform

Sensors ◽  
2018 ◽  
Vol 18 (7) ◽  
pp. 2362 ◽  
Author(s):  
Chengzhi Xiang ◽  
Ge Han ◽  
Yuxin Zheng ◽  
Xin Ma ◽  
Wei Gong
Keyword(s):  
Wavelet Transform ◽  
Carbon Cycle ◽  
Signal To Noise Ratio ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Signal Denoising ◽  
Differential Absorption ◽  
Lifting Wavelet Transform ◽  
Signal To Noise ◽  
Lifting Wavelet

Atmospheric CO2 plays an important role in controlling climate change and its effect on the carbon cycle. However, detailed information on the dynamics of CO2 vertical mixing remains lacking, which hinders the accurate understanding of certain key features of the carbon cycle. Differential absorption lidar (DIAL) is a promising technology for CO2 detection due to its characteristics of high precision, high time resolution, and high spatial resolution. Ground-based CO2-DIAL can provide the continuous observations of the vertical profile of CO2 concentration, which can be highly significant to gaining deeper insights into the rectification effect of CO2, the ratio of respiration photosynthesis, and the CO2 dome in urban areas. A set of ground-based CO2-DIAL systems were developed by our team and highly accurate long-term laboratory experiments were conducted. Nonetheless, the performance suffered from low signal-to-noise ratio (SNR) in field explorations because of decreasing aerosol concentrations with increasing altitude and surrounding interference according to the results of our experiments in Wuhan and Huainan. The concentration of atmospheric CO2 is derived from the difference of signals between on-line and off-line wavelengths; thus, low SNR will cause the superimposition of the final inversion error. In such a situation, an efficient and accurate denoising algorithm is critical for a ground-based CO2-DIAL system, particularly in field experiments. In this study, a method based on lifting wavelet transform (LWT) for CO2-DIAL signal denoising was proposed. This method, which is an improvement of the traditional wavelet transform, can select different predictive and update functions according to the characteristics of lidar signals, thereby making it suitable for the signal denoising of CO2-DIAL. Experiment analyses were conducted to evaluate the denoising effect of LWT. For comparison, ensemble empirical mode decomposition denoising was also performed on the same lidar signal. In addition, this study calculated the coefficient of variation (CV) at the same altitude among multiple original signals within 10 min and then performed the same calculation on the denoised signal. Finally, high-quality signal of ground-based CO2-DIAL was obtained using the LWT denoising method. The differential absorption optical depths of the denoised signals obtained via LWT were calculated, and the profile distribution information of CO2 concentration was acquired during field detection by using our developed CO2-DIAL systems.

scholarly journals A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

2020 ◽  
Author(s):  
Edward Malina ◽  
Jan-Peter Muller ◽  
David Sellers Walton
Keyword(s):  
Surface Albedo ◽  
Analysis Method ◽  
Satellite Measurements ◽  
School Students ◽  
Transport Models ◽  
Analysis Technique ◽  
Sensitivity Analysis Method ◽  
Total Column ◽  
Limited Sensitivity

Measurements of methane isotopologues can differentiate between different source types, be they biogenic (e.g. marsh lands) or abiogenic (e.g. industry). Global measurements of these isotopologues would greatly benefit the current disconnect between top-down (knowledge from Chemistry Transport Models and satellite measurements) and bottom-up (in situ measurement inventories) methane measurements. However, current measurements of these isotopologues are limited to a small number of in situ studies and airborne studies. In this paper we investigate the potential for detecting the second most common isotopologue of methane ( 13 CH 4 ) from space using the Japanese Greenhouse Gases Observation Satellite (GOSAT) applying a quick and simple residual radiance analysis technique. The method allows for a rapid analysis of spectral regions, and can be used to teach University students or advanced school students about radiative transfer analysis. Using this method we find limited sensitivity to 13 CH 4 , with detections limited to total column methane enhancements of >6%, assuming a desert surface albedo of >0.3.

SYMBOL RATE. ESTIMATION BOUNDS

2021 ◽  
Author(s):  
Е.А. БРУСИН
Keyword(s):  
Performance Evaluation ◽  
Lower Bound ◽  
Signal To Noise Ratio ◽  
Observation Interval ◽  
Spectral Characteristics ◽  
Interval Duration ◽  
Signal To Noise ◽  
Rate Estimation ◽  
Estimation Performance ◽  
Symbol Rate

В статье обсуждаются проблемы оценивания символьной частоты и определения эффективности получаемых оценок. Предложенный подход позволяет определить границы оценивания символьной частоты для сигналов различных видов модуляции и спектральныххарактеристик. Получено аналитическое выражение для нормированной модифицированной нижней границы Крамера-Рао оценивания символьной частоты для сигналов с косинусным скруглением. Представлены зависимости соответствующих границ от коэффициента скругления, отношения сигнал/шум на символ и длительности интервала наблюдения. The article discusses the problems of symbol rate estimation and the estimation performance evaluation. The proposed approach allows us to determine the symbol rate estimation bounds for signals of various types of modulation and various spectral characteristics. An analytical expression for the symbol rate modified Kramer-Rao lower bound is obtained for signals with root raised cosine spectrum. The dependences of the corresponding boundaries on the roll-off factor, the signal-to-noise ratio per symbol, and the observation interval duration are presented.

scholarly journals A scanning strategy optimized for signal-to-noise ratio for the Geostationary Carbon Cycle Observatory (GeoCarb) instrument

2019 ◽  
Vol 12 (6) ◽  
pp. 3317-3334 ◽  
Author(s):  
Jeffrey Nivitanont ◽  
Sean M. R. Crowell ◽  
Berrien Moore III
Keyword(s):  
North America ◽  
South America ◽  
Carbon Cycle ◽  
Signal To Noise Ratio ◽  
Signal To Noise ◽  
Scanning Strategy ◽  
Entire Area ◽  
Area Of Interest ◽  
Noise Ratio ◽  
Tropical South America

Abstract. The Geostationary Carbon Cycle Observatory (GeoCarb) will make measurements of greenhouse gases over the contiguous North and South American landmasses at daily temporal resolution. The extreme flexibility of observing from geostationary orbit induces an optimization problem, as operators must choose what to observe and when. The proposed scanning strategy for the GeoCarb mission tracks the sun's path from east to west and covers the entire area of interest in five coherent regions in the order of tropical South America east, tropical South America west, temperate South America, tropical North America, and temperate North America. We express this problem in terms of a geometric set cover problem, and use an incremental optimization (IO) algorithm to create a scanning strategy that minimizes expected error as a function of the signal-to-noise ratio (SNR). The IO algorithm used in this studied is a modified greedy algorithm that selects, incrementally at 5 min intervals, the scanning areas with the highest predicted SNR with respect to air mass factor (AF) and solar zenith angle (SZA) while also considering operational constraints to minimize overlapping scans and observations over water. As a proof of concept, two experiments are performed applying the IO algorithm offline to create an SNR-optimized strategy and compare it to the proposed strategy. The first experiment considers all landmasses with equal importance and the second experiment illustrates a temporary campaign mode that gives major urban areas greater importance weighting. Using a simple instrument model, we found that there is a significant performance increase with respect to overall predicted error when comparing the algorithm-selected scanning strategies to the proposed scanning strategy.

scholarly journals A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

2021 ◽  
Vol 2 ◽  
Author(s):  
Edward Malina ◽  
Jan-Peter Muller ◽  
David Walton
Keyword(s):  
Surface Albedo ◽  
Analysis Method ◽  
Satellite Measurements ◽  
School Students ◽  
Transport Models ◽  
Analysis Technique ◽  
Sensitivity Analysis Method ◽  
Total Column ◽  
Limited Sensitivity

Measurements of methane isotopologues can differentiate between different source types, be they biogenic (e.g. marsh lands) or abiogenic (e.g. industry). Global measurements of these isotopologues would greatly benefit the current disconnect between ‘top-down’ (knowledge from chemistry transport models and satellite measurements) and ‘bottom-up’ (in situ measurement inventories) methane measurements. However, current measurements of these isotopologues are limited to a small number of in situ studies and airborne studies. In this paper we investigate the potential for detecting the second most common isotopologue of methane (13CH4) from space using the Japanese Greenhouse Gases Observing Satellite applying a quick and simple residual radiance analysis technique. The method allows for a rapid analysis of spectral regions, and can be used to teach university students or advanced school students about radiative transfer analysis. Using this method we find limited sensitivity to 13CH4, with detections limited to total column methane enhancements of >6%, assuming a desert surface albedo of >0.3.

scholarly journals Commission 26 : Double and Multiple Stars

1991 ◽  
Vol 21 (1) ◽  
pp. 243-246
Author(s):  
H.A. McAlister
Keyword(s):  
Observational Study ◽  
Hubble Space Telescope ◽  
Selection Effects ◽  
Signal To Noise ◽  
Space Telescope ◽  
Double Stars ◽  
Multiple Stars ◽  
Coherent Field ◽  
Double And Multiple Stars ◽  
Precision And Accuracy

The observational study of double and multiple stars is traditionally seen as comprised of several specialized subfields, each defined by particular observational selection effects. Improvements in increased precision and accuracy, higher resolution, higher signal-to-noise ratios, greater sensitivity etc.), are leading the study of double stars to a truly coherent field. Significant advances in ground-based spectroscopy and interferometry provide a framework from which we can prepare for the future. The contributions to be made from space are currently in a state of uncertainty as we await results from the Hubble Space Telescope and Hipparcos.

scholarly journals Source brightness fluctuation correction of solar absorption Fourier Transform mid infrared spectra

2011 ◽  
Vol 4 (1) ◽  
pp. 443-459
Author(s):  
T. Ridder ◽  
T. Warneke ◽  
J. Notholt
Keyword(s):  
Spectral Region ◽  
Near Infrared ◽  
Trace Gas ◽  
Solar Absorption ◽  
Mid Infrared ◽  
Infrared Spectral Region ◽  
Infrared Spectral ◽  
Brightness Fluctuation ◽  
Precision And Accuracy ◽  
Total Column

Abstract. Solar absorption Fourier Transform infrared spectrometry is considered a precise and accurate method for the observation of trace gases in the atmosphere. The precision and accuracy of such measurements are dependent on the stability of the light source. Fluctuations in the source brightness reduce the precision and accuracy of the trace gas concentrations, but cannot always be avoided. Thus, a strong effort is made within the community to reduce the impact of source brightness fluctuations by applying a correction on the spectra following the measurements. So far, it could be shown that the precision and accuracy of CO2 total column concentrations could be improved by applying a source brightness fluctuation correction to spectra in the near infrared spectral region. The analysis of trace gas concentrations obtained from spectra in the mid infrared spectral region is fundamental. However, spectra below 2000 cm−1 are generally considered uncorrectable, if they are measured with a MCT detector. Such measurements introduce an unknown offset to MCT interferograms, which prevents a source brightness fluctuation correction. Here, we show a method of source brightness fluctuation correction, which can be applied on spectra in the whole infrared spectral region including spectra measured with a MCT detector. We present a solution to remove the unknown offset in MCT interferograms allowing MCT spectra for an application of source brightness fluctuation correction. This gives an improvement in the quality of MCT spectra and we demonstrate an improvement in the retrieval of O3 profiles and total column concentrations. For a comparison with previous studies, we apply our source brightness fluctuation correction method on spectra in the near infrared spectral region and show an improvement in the retrieval of CO2 total column concentrations.

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