Retrieval, Validations and Interpretation of Stratospheric Water Vapor Distributions from SCIAMACHY Lunar Occultation Measurements

Water vapor is a unique atmospheric component, its distribution directly influences the chemistry and dynamics in different parts of the atmosphere. Water vapor observations from satellite borne instruments provide information on its long term seasonal and inter-annual variabilities and are important for climate projections and predictions. In the polar stratosphere, the water vapor amounts control the polar vortex temperatures and the formation temperature of the polar stratospheric clouds (PSCs). Water vapor has a strong relationship with the circulation and transport features related to polar vortex and its amounts define the Formation and deposition of PSCs. SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) aboard Envisat launched in 2002 has observed the Earth s atmosphere in nadir, limb and solar or lunar occultation geometry covering ultraviolet, visible and near ifrared (240-2830 nm) wavelength range at moderate spectral resolution. SCIAMACHY's measurements have provided total columns as well as vertical profiles of atmospheric constituents and climate parameters relevant to the ozone chemistry, air pollution and global climate change issues, from Troposphere upto the Mesosphere. This thesis contributes to exploit the lunar occultation spectra measured by SCIAMACHY at the local night time, with a latitudinal coverage of 56-89°S, to derive vertical stratospheric water vapor number density profiles in the altitude range of 17-50 km, from 2003 till 2010. The water vapor distributions are retrieved using the spectral window 1350-1420 nm in the near infrared region of the SCIAMACHY spectra. SCIATRAN version 3.0, a radiative transfer model and an inversion scheme based on optimal estimation (OE), is optimized and adapted for the retrieval. Within the inversion scheme, the residuals between the measured differential optical depths and the ones calculated by the forward model are in the order of 0.5%. The radiative transfer computation is performed using correlated-k method employing the exponential sum fitting of transmission function (ESFT) approximation instead of the detailed but computationally costly line by line (LBL) model. Since LBL is the most precise representative of reality, the ESFT database (pressure, temperature and coefficient grids) is optimized with an objective to achieve the closest agreement between the two approaches and to obtain a high quality retrieval product. The retrieval is observed to be highly sensitive to the numbers of coefficients in the ESFT grid. Extensive sensitivity studies and optimizations are performed for the key input parameters as slit function, signal to noise ratio, Tikhonov parameter and the climatological profiles to select their optimal values in the retrieval setting. To evaluate the quality of the retrieved lunar occultation water vapor product, validations are performed with collocated measurements from the satellite occultation instruments ACE-FTS and HALOE and the instruments measuring in limb geometry, MLS and MIPAS. In addition SCIAMACHY limb observations are also used for comparison. SCIAMACHY lunar occultation and ACE-FTS measurements agree within 7% on the average. With HALOE, the difference is around 5%. The validation of the coincident lunar occultation and the MLS measurements is exceptionally good with an agreement of 1.5-4% whereas that with MIPAS is in the range of 10%. The comparisons of the lunar occultation product with all the four instruments are found to be well within their reported biases. With the SCIAMACHY limb water vapor measurements, the differences are of the order of 4%. The validation results show that an excellent SCIAMACHY lunar occultation water vapor product is obtained. The dataset of water vapor distributions from SCIAMACHY lunar occultation measurements is expected to facilitate the understanding of physical and chemical processes in the southern mid-latitudes, the dynamical processes related to polar vortex and on the formation of PSCs, which can be studied through our product right at their onset as observed. The product will add as the southern hemispheric measurement coverage to the SCIAMACHY long term global water vapor time series

Mapping Informal Settlements in Developing Countries using Machine Learning and Low Resolution Multi-spectral Data

Informal settlements are home to the most socially and economically vulnerable people on the planet. In order to deliver effective economic and social aid, non-government organizations (NGOs), such as the United Nations Children's Fund (UNICEF), require detailed maps of the locations of informal settlements. However, data regarding informal and formal settlements is primarily unavailable and if available is often incomplete. This is due, in part, to the cost and complexity of gathering data on a large scale. To address these challenges, we, in this work, provide three contributions. 1) A brand new machine learning data-set, purposely developed for informal settlement detection. 2) We show that it is possible to detect informal settlements using freely available low-resolution (LR) data, in contrast to previous studies that use very-high resolution (VHR) satellite and aerial imagery, something that is cost-prohibitive for NGOs. 3) We demonstrate two effective classification schemes on our curated data set, one that is cost-efficient for NGOs and another that is cost-prohibitive for NGOs, but has additional utility. We integrate these schemes into a semi-automated pipeline that converts either a LR or VHR satellite image into a binary map that encodes the locations of informal settlements.Comment: Published at the AAAI/ACM Conference on AI, ethics and society. Extended results from our previous workshop: arXiv:1812.0081

Evaluating remote sensing methods of solar irradiance methods under the consideration of cloud variability

The accuracy of the irradiance remote sensing methods was evaluated for different classes of cloud variability

Variability class dependent evaluation of the CAMS Radiation Service

The Copernicus Atmospheric Monitoring Service (CAMS) offers Solar radiation services (CRS) providing information on surface solar irradiance (SSI). The service is currently derived from Meteosat Second Generation (MSG) and the service evolution includes its extension to other parts of the globe. CRS provides clear and all sky time series combining satellite data products with numerical model output from CAMS on aerosols, water vapour and ozone. These products are available from 2004 until yesterday. A regular quality control of input parameters, quarterly benchmarking against ground measurements and automatic consistency checks ensure the service quality. Variability of solar surface irradiances in the 1-minute range is of interest especially for solar energy applications. The variability classes can be defined based on ground as well as satellite-based measurements. This study will present the evaluation of the CAMS CRS based on the eight variability classes derived from ground observations of direct normal irradiation (DNI) (Schroedter-Homscheidt et al., 2018). Such an analysis will help assess the impact of recent improvements in the derivation of all sky irradiance under different cloudy conditions. References: Schroedter-Homscheidt, M., S. Jung, M. Kosmale, 2018: Classifying ground-measured 1 minute temporal variability within hourly intervals for direct normal irradiances. – Meteorol. Z. 27, 2, 160–179. DOI:10.1127/metz/2018/0875

Improving the satellite retrieval of surface solar irradiance during an eclipse

Solar eclipse causes high magnitude fluctuations in the Surface Solar Irradiance (SSI) for a short duration and consequently reduces the output of solar PV systems. Grid operators try to estimate the impending loss in PV power generation prior to the occurrence of an eclipse in order to schedule conventional generators for compensating the loss. The worldwide installed capacity of grid connected solar PV systems is expected to steeply rise in the coming decade as a result of the various policy initiatives aimed to tackle the climate change. In future electric supply networks with a high penetration of solar PV systems, such large ramps in generation could impact the stability of the network. Although a solar eclipse is a purely deterministic phenomenon, it’s impact on the satellite retrieval of Surface Solar Irradiance (SSI) is complicated due to the possibility of cloud presence in the regions affected by the eclipse. The extraterrestrial solar irradiance is reduced by the moon during an eclipse. On the one hand this causes clouds to appear darker and they get assigned lower reflectance values than they should have in reality. This leads to predicting higher values for the solar irradiance under these clouds than expected. On the other hand, the eclipse also reduces the clear sky irradiance reaching the earth surface. We developed a method to make corrections for both of these effects on the High Resolution Visible (HRV) channel images from Meteosat-11 The results are validated against ground measurements of irradiance provided by BSRN, IEA-PVPS, DTN and the National Weather Services networks. The validation is performed for sites with locations across Europe and for the last two eclipses

The SPARC water vapour assessment II: comparison of annual, semi-annual and quasi-biennial variations in stratospheric and lower mesospheric water vapour observed from satellites

In the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), the amplitudes and phases of the annual, semi-annual and quasi-biennial variation in stratospheric and lower mesospheric water were compared using 30 data sets from 13 different satellite instruments. These comparisons aimed to provide a comprehensive overview of the typical uncertainties in the observational database which can be considered in subsequent observational and modelling studies. For the amplitudes, a good agreement of their latitude and altitude distribution was found. Quantitatively there were differences in particular at high latitudes, close to the tropopause and in the lower mesosphere. In these regions, the standard deviation over all data sets typically exceeded 0.2 ppmv for the annual variation and 0.1 ppmv for the semi-annual and quasi-biennial variation. For the phase, larger differences between the data sets were found in the lower mesosphere. Generally the smallest phase uncertainties can be observed in regions where the amplitude of the variability is large. The standard deviations of the phases for all data sets were typically smaller than a month for the annual and semi-annual variation and smaller than 5 months for the quasi-biennial variation. The amplitude and phase differences among the data sets are caused by a combination of factors. In general, differences in the temporal variation of systematic errors and in the observational sampling play a dominant role. In addition, differences in the vertical resolution of the data, the considered time periods and influences of clouds, aerosols as well as non-local thermodynamic equilibrium (NLTE) effects cause differences between the individual data sets

The SPARC water vapour assessment II: biases and drifts of water vapour satellite data records with respect to frost point hygrometer records

Satellite data records of stratospheric water vapour have been compared to balloon-borne frost point hygrometer (FP) profiles that are coincident in space and time. The satellite data records of 15 different instruments cover water vapour data available from January 2000 through December 2016. The hygrometer data are from 27 stations all over the world in the same period. For the comparison, real or constructed averaging kernels have been applied to the hygrometer profiles to adjust them to the measurement characteristics of the satellite instruments. For bias evaluation, we have compared satellite profiles averaged over the available temporal coverage to the means of coincident FP profiles for individual stations. For drift determinations, we analysed time series of relative differences between spatiotemporally coincident satellite and hygrometer profiles at individual stations. In a synopsis we have also calculated the mean biases and drifts (and their respective uncertainties) for each satellite record over all applicable hygrometer stations in three altitude ranges (10–30 hPa, 30–100 hPa, and 100 hPa to tropopause). Most of the satellite data have biases <10 % and average drifts <1 % yr−1 in at least one of the respective altitude ranges. Virtually all biases are significant in the sense that their uncertainty range in terms of twice the standard error of the mean does not include zero. Statistically significant drifts (95 % confidence) are detected for 35 % of the ≈ 1200 time series of relative differences between satellites and hygrometers

Retrieval, Validation und Interpretation der Stratosphärischen Wasserdampfverteilung aus SCIAMACHY Mondokkultationsmessungen

Water vapor is a unique atmospheric component, its distribution directly influences the chemistry and dynamics in different parts of the atmosphere. Water vapor observations from satellite borne instruments provide information on its long term seasonal and inter-annual variabilities and are important for climate projections and predictions. In the polar stratosphere, the water vapor amounts control the polar vortex temperatures and the formation temperature of the polar stratospheric clouds (PSCs). Water vapor has a strong relationship with the circulation and transport features related to polar vortex and its amounts define the Formation and deposition of PSCs. SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) aboard Envisat launched in 2002 has observed the Earth s atmosphere in nadir, limb and solar or lunar occultation geometry covering ultraviolet, visible and near ifrared (240-2830 nm) wavelength range at moderate spectral resolution. SCIAMACHY's measurements have provided total columns as well as vertical profiles of atmospheric constituents and climate parameters relevant to the ozone chemistry, air pollution and global climate change issues, from Troposphere upto the Mesosphere. This thesis contributes to exploit the lunar occultation spectra measured by SCIAMACHY at the local night time, with a latitudinal coverage of 56-89°S, to derive vertical stratospheric water vapor number density profiles in the altitude range of 17-50 km, from 2003 till 2010. The water vapor distributions are retrieved using the spectral window 1350-1420 nm in the near infrared region of the SCIAMACHY spectra. SCIATRAN version 3.0, a radiative transfer model and an inversion scheme based on optimal estimation (OE), is optimized and adapted for the retrieval. Within the inversion scheme, the residuals between the measured differential optical depths and the ones calculated by the forward model are in the order of 0.5%. The radiative transfer computation is performed using correlated-k method employing the exponential sum fitting of transmission function (ESFT) approximation instead of the detailed but computationally costly line by line (LBL) model. Since LBL is the most precise representative of reality, the ESFT database (pressure, temperature and coefficient grids) is optimized with an objective to achieve the closest agreement between the two approaches and to obtain a high quality retrieval product. The retrieval is observed to be highly sensitive to the numbers of coefficients in the ESFT grid. Extensive sensitivity studies and optimizations are performed for the key input parameters as slit function, signal to noise ratio, Tikhonov parameter and the climatological profiles to select their optimal values in the retrieval setting. To evaluate the quality of the retrieved lunar occultation water vapor product, validations are performed with collocated measurements from the satellite occultation instruments ACE-FTS and HALOE and the instruments measuring in limb geometry, MLS and MIPAS. In addition SCIAMACHY limb observations are also used for comparison. SCIAMACHY lunar occultation and ACE-FTS measurements agree within 7% on the average. With HALOE, the difference is around 5%. The validation of the coincident lunar occultation and the MLS measurements is exceptionally good with an agreement of 1.5-4% whereas that with MIPAS is in the range of 10%. The comparisons of the lunar occultation product with all the four instruments are found to be well within their reported biases. With the SCIAMACHY limb water vapor measurements, the differences are of the order of 4%. The validation results show that an excellent SCIAMACHY lunar occultation water vapor product is obtained. The dataset of water vapor distributions from SCIAMACHY lunar occultation measurements is expected to facilitate the understanding of physical and chemical processes in the southern mid-latitudes, the dynamical processes related to polar vortex and on the formation of PSCs, which can be studied through our product right at their onset as observed. The product will add as the southern hemispheric measurement coverage to the SCIAMACHY long term global water vapor time series

An Analysis of the Risk Factors for the Development of Parastomal Hernia: A Single Institutional Experience.

OBJECTIVES  To study the frequency of risk factors affecting the development of parastomal hernias in patients undergoing stoma formation. STUDY DESIGN A retrospective descriptive cross-sectional study. Duration of Study: This study was conducted at the Department of General Surgery between January 2017 to December 2020. METHODOLOGY  A total of 163 patients aged between 20 and 100 years and who required a stoma formation were included in the study. The patients with incomplete data and those lacking post-operative imaging were excluded. According to this selection criteria, 80 patients were excluded. The data was collected for all patients from the hospital database. This included patient's demographic information, co-morbidities, pre-surgery patient characteristics, an indication of stoma formation, the location of stoma exit, type of surgery, associated comorbidities, subcutaneous fat thickness, and type of stoma formed. Data were analyzed using IBM Corp. Released 2019. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp. RESULTS  The mean age was 68.46 ± 16.50 years, with males in the majority: 48 (57.8%). Most of the patients, 53 (63.8%), had malignant disease. Post-stoma formation, a total of 38 (45.9%) patients developed parastomal hernias, mostly involving the sigmoid colon (n=62, 74.7%). However, there was a statistically significant relationship between paroxysmal sympathetic hyperactivity (PSH) incidence with non-trans-rectus stomas (trans-oblique n=07, junctional n=28) (OR 3.04, CI 1.23-7.5, p=0.014). Furthermore, malignancy was also not an independent predictor of PSH (OR 0.408, CI 0.15-1.2, p=0.056). All other risk factors included in this study were nonsignificant. CONCLUSION  Our study shows that the incidence of parastomal hernias is rising with a high rate demonstrated in our patients. There was no statistically significant association between patient-related preoperative and operative factors with increased risk of parastomal hernias in our population except for a non-trans-rectus stoma, which was identified as an independent risk factor for parastomal hernias. Based on our findings, we would recommend a trans-rectus stoma over all other stoma sites. However, a much larger study is needed to validate this finding further