Daily composite wind fields from Oceansat-2 scatterometer

Oceansat-2 scatterometer (OSCAT) is an active microwave sensor, intended to provide ocean surface wind vectors over the global oceans. In the present work, an attempt has been made to generate daily composites of OSCAT Level-3 (L3) wind vectors using Data-Interpolating Variational Analysis (DIVA) method from ascending and descending passes over the Indian Ocean region. This could be useful for operational purposes and in generating value-added products like wind stress and curl of wind stress. The daily composite wind vectors of zonal (U) and meridional (V) components have been validated by comparing with Advanced Scatterometer (ASCAT) and wind from in situ buoys for the year 2012. Wind composites thus generated using DIVA are found to match well with in situ, and ASCAT wind products. Minor deviations are observed with respect to ASCAT wind, which could be attributed to the difference in interpolation techniques used for the two scatterometer products. Given that the repeat period of ASCAT is 5 days and that of OSCAT is only 2 days, OSCAT wind products could be conveniently used for real-time met-ocean studies.     

Comparison of oceanic winds measured by space-borne scatterometers and altimeters

Global ocean surface wind speeds from Quick Scatterometer (QuikSCAT) for 5 years (2005–2009) and from Oceansat-2 Scatterometer (OSCAT) for 1 year (2010) were compared with wind speeds estimated from JASON Altimeters for representative months to investigate the consistency in wind speeds between these sensors. The comparison was carried out through statistical analyses. The spatial window used for comparison with JASON was 0.25° for QuikSCAT and 0.5° for OSCAT, while the temporal window for both QuikSCAT and OSCAT was ±30 min. The results of the inter-comparison indicate that OSCAT wind speeds are almost as consistent with JASON as QuikSCAT wind speeds.     

Validation of ocean surface winds from the OCEANSAT-2 scatterometer using triple collocation

Ocean surface winds from the OCEANSAT-2 scatterometer (OSCAT) were validated with equivalent neutral wind observations from 87 global buoys and winds from the European Centre for Medium Range Weather Forecasting (ECMWF) Numerical Weather Prediction (NWP) model using triple collocation for a period of 9 months. Functional relationship analysis (FRA) employing the error-in-variables method is found to be more ‘exact’ in comparison with classical linear regression analysis for the validation of the OSCAT data. Moreover, using the wind component domain for validation and error assessment rather than the speed and direction domain is confirmed to be favourable. The FRA method applied on the triple-collocated wind components shows that the error standard deviations of the OSCAT and buoy winds are quite similar. The calibration trends and biases for OSCAT, buoys and ECMWF are found to be close to unity and zero, respectively.     

Physical retrieval of tropical ocean surface wind speed under rain-free conditions using spaceborne microwave radiometers

This research proposes a physical algorithm for retrieving sea surface wind speed using a combination of passive microwave satellite observations and simulations, namely Advanced Microwave Scanning Radiometer (AMSR-E) observations for vertical polarization, and a simulation based on the fast Radiative Transfer for TOVS with Global Data Assimilation System data for horizontal polarizations. A regression relationship between sea surface roughness and sea surface wind speed was derived using the Hong approximation and polarization ratio near Brewster’s angle. The sea surface wind speed algorithm was assessed using the AMSR-E data. Comparing sea surface wind speed from the proposed algorithm using AMSR-E 6.925, 10.65, and 18.7 GHz data with Tropical Atmospheric Ocean (TAO) data from 1 January 2010 to 31 December 2010 shows that the estimated bias and root mean square error (RMSE) were ?0.126 and 1.191 ms^?1, ?0.094 and 1.152 ms^?1, and ?0.085 and 1.338 ms^?1, respectively. The current official AMSR-E sea surface wind speed shows the bias and RMSE were ?0.614 and 1.330 ms^?1, respectively, when compared with TAO buoy observations, which was similar to those of the proposed algorithm using AMSR-E 18.7 GHz. This study provides a useful sea surface wind speed retrieval algorithm with high accuracy on the sea surface, which can be applied to a variety of spaceborne passive microwave radiometers.     

Validation of wind speed retrieval from RISAT-1 SAR images of the North Indian Ocean

An algorithm has been developed to retrieve ocean surface wind speed from Synthetic Aperture Radar (SAR) on-board Radar Imaging Satellite-1 (RISAT-1). The retrieved wind speed is subsequently validated using observations from Advanced Scatterometers (on-board Metop-A, Metop-B) for the period from July 2012 to September 2016. The quality of the retrieved wind speed was assessed using observations from offshore moored buoys in the Bay of Bengal and Arabian Sea. It has been observed that the RISAT-1 derived wind speed, retrieved using three Geophysical Model Functions (GMFs) viz., CMOD5.N, CMOD5 and CMOD_IFR2 are negatively biased relative to ASCAT as well as Buoy. The biases with ASCAT are 0.38 (0.98) ms^?1, 0.96 (1.24) ms^?1 and 1.31 (1.55) ms^?1 respectively for the coastal (offshore) region. The Root Mean Square Difference (RMSD) between RISAT-1 and ASCAT are 1.58 (1.78), 1.8 (1.85) and 1.96 (1.99) in m s^?1 respectively for coastal (offshore) waters, which is well within the acceptable limits. Thus it is found that the quality of the wind speed retrieved using CMOD5.N GMF is better than other GMFs. The high resolution wind data available from RISAT-1 SAR opens new pathways for assessing wind energy potential along the Indian coast.     

Observation of diurnal variations in mesoscale eddy sea-surface currents using GOCI data

The surface current field of a mesoscale eddy in the East Sea (Sea of Japan) was derived from consecutive Geostationary Ocean Color Imager chlorophyll-a (chl-a) concentration images using the normalized maximum cross-correlation method. The estimated current field of the eddy exhibited anticyclonic structure demonstrated by the objective dynamic thresholds of correlation coefficients. The eddy periphery was defined by fitting an ellipse to subjectively selected points from the frontal map of chl-a concentration data. Radial distribution and hourly variation of the current speed around the eddy were presented. In terms of the magnitude and direction, the estimated current field was in good agreement with altimeter-based current field and current vectors from surface drifters. Diurnal variations in the current speeds of the mesoscale eddies showed a quadratic relation to the wind speed.     

A test of a sun glint correction method for the near-3.9 μm channels of the FengYun-3D Hyperspectral InfraRed Atmospheric Sounder (HIRAS)

ABSTRACT

The Hyperspectral InfraRed Atmospheric Sounder (HIRAS), the first Chinese sun-synchronous hyperspectral infrared sounder onboard FengYun 3D (FY-3D), was launched on 15 November 2017. It will play a significant role in improving forecast accuracy of numerical weather prediction (NWP) systems. However, sun glint effects on the FY-3D HIRAS 3.9 μm channels cannot be currently estimated by radiative transfer models. In this study, a new method for quantifying sun glint effects has been developed through a cubic fitting relationship between sun glint angles and the observed brightness temperature minus simulated brightness temperature (O ? B) after bias correction. The results show that the brightness temperatures of channel 2275 (2550 cm^?1) are higher over the ocean between 40°S and 40°N within areas of sun glint angle less than 40°; in these regions, O ? B values can reach 10 K during the daytime. Daytime global mean clear-sky O ? B biases from channel 2035 (2400 cm^?1) to channel 2275 (2550 cm^?1) increase gradually from 0 to 2.5 K. In contrast, daytime O ? B biases after sun glint correction are within ±0.2 K, indicating that the corrected radiances are suitable to be assimilated into NWP systems.     

Branch Reports

ABSTRACT:

This study investigated the accuracy of two animal specific non-contact infrared thermometers (Rycom and Thermofocus) when compared to rectal temperature in healthy horses. One hundred rectal and eye temperatures were measured in 22 horses. Fewer than 50% of the readings taken with the Thermofocus device were within ±?0.5°C of rectal temperature. Over 80% of eye temperature readings taken with the Rycom device were within ±?0.5°C of rectal temperature measured from the medial canthus region. The Rycom thermometer also appears to detect hyperthermia when measuring the left eye temperature; however, clinical patient testing is needed before its use can be recommended.     

Agreement between monthly land rainfall estimates from TRMM-PR and gauge-based observations over South Asia

There is a demand for reliable rainfall data-set over the South Asia region covering both land and ocean for model validation/development and various applications. For satellite rainfall estimates (SREs), the algorithm development groups also need validation information on SRE. The Tropical Rainfall Measuring Mission (TRMM) project has produced recently improved version 7 (V7) rainfall data-sets. Version 6 (V6) and V7 of 3A25, the surface rainfall products derived from TRMM precipitation radar (PR), are compared with gauge-based observations at 0.5° latitude/longitude resolution for the period of 1998–2007 over the South Asian land region. Both 3A25V7 and 3A25V6 represent the mean rainfall distribution patterns reasonably well. However, 3A25 products overestimate rainfall over the Indonesian region compared to gauge-based data. For some parts of South Asia, SREs show considerable difference in the magnitude of coefficient of variation compared to gauge-based information. At seasonal scale, a contrasting feature in bias over India during the pre-monsoon and monsoon seasons is noticed from both the versions of 3A25 data-set. In general, 3A25 rainfall data-sets are able to capture the interannual variability of rainfall over South Asia. The frequency distribution of monthly rainfall rate reveals that 3A25 products marginally underestimate rainfall below 10 mm day^?1 and overestimate higher rainfall rate compared to gauge-based data. Overall, 3A25V7 product is marginally better than its previous version (3A25V6) over the South Asian land region.     

Merging gauge data and models with satellite data from multiple sources to aid the understanding of long-term trends in chlorophyll-a concentrations

Several studies have analysed the long-term trends of chlorophyll-a (chl-a) concentration and related its intensity to sea surface temperature (SST) and wind forcing. In this article, we present trends of chl-a concentrations for the period 1997–2016 derived from multi-merged satellite data and analysed the role of SST, wind mixing (WM) and surface incoming short wave flux (SISF) and river discharges in the distribution of chl-a in the coastal waters of southwest India. The results show decreasing trend of anomalies for chl-a. Chl-a shows negative trend, though not significant, with all other variables, i.e., WM, SISF and river discharge over the last two decades in the study area. Whereas, an increasing trend of SST has recorded for the region during the same period. Our results suggest that the warming of sea surface as observed from SST, decreased river input, weakening of winds and reduced solar radiation are among the most prominent reasons for decline in chl-a concentration for the study region. Further, the positive relation between chl-a with WM and SISF and negative correlation with SSTs suggest that these trends are driven by enhanced ocean stratification due to rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers.     

Results of the Global WaterPack: a novel product to assess inland water body dynamics on a daily basis

The understanding and assessment of surface water variability of inland water bodies, for example, due to climate variability and human impact, requires steady and continuous information about its inter- and intra-annual dynamics. In this letter, we present an approach using dynamic threshold techniques and utilizing time series to generate a data set containing detected surface water bodies on a global scale with daily temporal resolution. Exemplary results for the year 2013 that were based on moderate resolution imaging spectroradiometer products are presented in this letter. The main input data sets for the presented product were MOD09GQ/MYD09GQ and MOD10A1/MYD10A1 with a spatial resolution of 250 m and 500 m, respectively. Using the static water mask MOD44W, we extracted training pixels to generate dynamic thresholds for individual data sets on daily basis. In a second processing step, the generated sequences of water masks were utilized to interpolate the results for any missing observations, either due to cloud coverage or missing data, as well as to reduce misclassification due to cloud shadow. The product provides an opportunity for further research and for assessing the drivers of changes of inland water bodies at a global scale.     

Captive Breeding and Embryonic Development of Butter Catfish (Ompok bimaculatus, Bloch 1794), a Threatened Fish of Indian Sub-continent in Northern India

The captive breeding of butter catfish (Ompok bimaculatus, Bloch 1794), a threatened silurid of Indian sub-continent was successfully carried out at the National Bureau of Fish Genetic Resources, Lucknow. Ten induced breeding trials conducted on the fish revealed that the fish can be naturally spawned in controlled conditions using sGnRH analogue and dopamine antagonist. The most suitable and economical dose estimated was 0.7 ml kg^?1 body weight for female and 0.5 ml kg^?1 for male. The latency period for spawning was 7–8 h at temperature 27 ± 0.5 °C and fertilization and hatching rates were found in the range of 75–90 % and 80–90 % respectively in flow-through system. The egg hatched out in 21 ± 1 h post fertilization (hpf) at temperature 27 ± 0.5 °C and yolk-sac was completely absorbed in 48 hpf. The larval survival reduced considerably after 5 days and was recorded 10.4 % after 10 days rearing, reason being, poor food acceptability and cannibalism. The fish responded well when injected with hormonal doses within 36 h of procurement from the pond but thereafter did not respond probably due to stress factor. These trials may be useful in standardizing the ex-situ breeding protocols for O. bimaculatus.     

Two-dimensional,threshold-based cloud type classification using MTSAT data

A new two-dimensional threshold diagram (2D-THR) has been developed based on maximum likelihood cloud classification results, which can readily be applied for Multi-functional Transport Satellite (MTSAT) split window datasets. Because 2D-THR was trained using northern summer 2010 data for Japan and its surrounding area, it is typically suitable only for summer. Comparison of snapshot cloud type distributions showed that 2D-THR images and the corresponding night-time microphysical colour composite images as well as 2D-THR images and Japan Meteorological Agency (JMA) cloud type images are in good agreement. A time series inter-comparison of the hourly 2D-THR cloud classification results with the JMA cloud type classification data product was performed by calculating spatial correlation of cloud percentage for 1°?×?1° grid cells. For cumulonimbus, high-level, middle-level and low-level clouds over tropical and subtropical areas in the northwestern Pacific Ocean region, the spatial correlation between 2D-THR and JMA is moderate. Thus, 2D-THR cloud classification algorithm can be applied in both regions.     

Subtropical gyre variability as seen from satellites

A satellite multi-sensor approach is used to analyse the biological response of open ocean regions of the subtropical gyres to changes in physical forcing. Thirteen years (1998–2010) of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll-a (chl-a) data, combined with concurrent satellite records of sea-surface temperature (SST) and sea level height, were analysed to investigate the seasonal and inter-annual variability of chl-a concentration within these immense so-called ocean deserts. The seasonal variability of chl-a within the gyres is driven mostly by the warming/cooling of surface waters. Summer warming promotes shallower mixed layers and lower chl-a due to a reduction of vertical mixing and consequently a decrease in nutrient supply. The opposite happens during the winter cooling period. Therefore, long-term trends in SST have the potential to cause an impact on the inter-annual variability of chl-a. Our analyses show that, during the 13 whole years of SeaWiFS data record, the North Pacific, Indian Ocean and North Atlantic gyres experienced a decrease in chl-a of 9%, 12% and 11%, respectively, with corresponding SST increases of 0.27°C, 0.42°C and 0.32°C, respectively. The South Pacific and South Atlantic gyres also showed warming trends but with weak positive trends in chl-a that are not statistically significant. We hypothesize that the warming of surface waters in these two gyres is counterbalanced by other interacting physical- and biological-driving mechanisms, as indicated in previous studies.     

Study on the effects of some factors that affect sea surface emissivity retrievals

The first aim of this article is to study the impact of some factors (effective wavelength, temperature, and aerial average emission angle) on sea surface emissivity (SSE) retrievals. It is well known that SSE is weakly influenced by these factors when we consider that each one of them acts independently from the others. However, taking them together, these factors are highly significant. The calculation of SSE including these factors has clearly brought out a high level of concordance between a theoretical model and in situ measurements for a wavelength of 11.0 µm especially at observation angles of 55° and 65° for wind speeds of 5 and 10 m s^?1. Wavelengths 8.7 and 12.0 µm also show, in most cases, a near to 0.000 or a negligible negative bias for an observation angle up to 55°. At wavelength 12 µm, the viewing angle of 65° seems to be questionable due to some inconsistencies and element of physics not well determined in practical terms.     

Land cover in Upper Egypt assessed using regional and global land-cover products derived from MODIS imagery

Irrigation along the Nile River has resulted in dramatic changes in the biophysical environment of Upper Egypt. In this study we used a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m Normalized Difference Vegetation Index data and Landsat imagery to identify areas that changed from 2001 to 2008 as a result of irrigation and water-level fluctuations in the Nile River and nearby waterbodies. We used two different methods of time series analysis – principal components analysis (PCA) and harmonic decomposition – applied to the MODIS 250 m Normalized Difference Vegetation Index images to derive simple three-class land-cover maps and then assessed their accuracy using a set of reference polygons derived from 30 m Landsat 5 and 7 imagery. We analysed our MODIS 250 m maps against a new MODIS global land-cover product (MOD12Q1 collection 5) to assess whether regionally specific mapping approaches are superior to a standard global product. Results showed that the accuracy of the PCA-based product was greater than the accuracy of either the harmonic decomposition or MOD12Q1 products for the years 2001, 2003 and 2008. However, the accuracy of the PCA product was only slightly better than the MOD12Q1 for 2001 and 2003. Overall, the results suggest that our PCA-based approach produces a high level of user and producer accuracies, although the MOD12Q1 product also showed consistently high accuracy. Overlay of 2001–2008 PCA-based maps showed a net increase of 12,129 ha of irrigated vegetation, with the largest increase found from 2006 to 2008 around the districts of Edfu and Kom Ombo. This result was unexpected in light of ambitious government plans to develop 336,000 ha of irrigated agriculture around the Toshka Lakes.     

The consistency of myocardial strain derived from heart deformation analysis

The purpose of this study was to assess the consistency of semi-automated myocardial strain analysis by prototype software across field strengths, temporal resolutions, and examinations. 35 volunteers (48?±?13 years; 20% women) and 25 patients (54?±?12 years; 44% women) without significant cardiac dysfunction underwent cine cardiac magnetic resonance imaging (CMR) at 1.5 T with a temporal resolution of 39.2 msec. 34 subjects also underwent imaging at 3.0 T; 16 had repeat examinations within 14 days; and 9 underwent CMR with temporal resolutions of 12.5 and 39.2 msec on the same day. Prototype heart deformation analysis (HDA) software was used to retrospectively quantify strain from segmented balanced steady state free precession (bSSFP) cinegraphic images. Myocardial contours were automatically generated on short axis images and drawn at end-diastole by two independent reviewers on long-axis images. Contours were automatically propagated throughout the cardiac cycle. Global and regional peak systolic strain were compared across observers, field strengths, temporal resolutions, and examinations. Inter-observer agreement was excellent (ICC?>?0.87, p?<?0.01). Inter-examination variability was low, ranging from 1.7 (1.0–2.4)% to 2.5 (1.9–3.1)%, except for radial strain: 9.2 (7.6–10.5)%. Most global and regional strain values were not significantly different across field strengths and temporal resolutions (p?>?0.05). Normal global peak systolic strain values with HDA were ?25.0 (?24.0 to ?26.1)% (LV circumferential), 60.5 (55.3 to 65.6)% (LV radial), ?22.3 (?20.5 to ??24.0)% (LV longitudinal), and ?26.0 (?23.8 to ?28.2)% (RV longitudinal). HDA prototype software enabled efficient and consistent quantification of myocardial strain from conventional bSSFP cine CMR data, demonstrating clinical feasibility.     

Examination of femoral-neck structure using finite element model and bone mineral density using dual-energy X-ray absorptiometry

BackgroundResearch regarding femoral-neck fractures has mainly focused on bone mineral density and limited studies have been performed on relationship between the femoral-neck structure and its fracture.MethodsFinite element models were established to estimate stress distributions across the femoral neck with various femoral-neck angle from 115° to 140°. The bone mineral density measurements across the femoral-neck region using dual-energy X-ray absorptiometry were taken from 89 healthy and 10 patients with a femoral-neck fracture. Femoral neck angles were determined on radiographs from a separate group of participants.FindingsThe results showed that the bone mineral density of the fracture patients was significantly smaller in all examined areas around femoral neck, especially in the ward’s triangle. Under a same loading condition, the stress level may easily reach its intensity limit and therefore cause a fracture. The modeling results indicated that the posteromedial side of the femoral neck experienced the highest stress and was inversely related with the femoral-neck angle. As the angle decreased below 125°, the stress around the femoral neck increased significantly and therefore increases risk of fracture at the site.InterpretationsIt is recommended that if the femoral-neck angle is below 125° and is accompanied by low bone mineral density, the patient should be considered a high risk candidate for femoral-neck fracture. In addition, if the femoral-neck angle of one hip is significantly smaller than the other side and 125°, the hip should be also considered as high risk.     

High Pyridine Generation in Ceftazidime-Icodextrin Admixtures Used to Treat Peritoneal Dialysis-associated Peritonitis

PurposeTo investigate the amount of pyridine generated from degradation of ceftazidime in icodextrin peritoneal dialysis (PD) solutions.MethodsPD solutions that contained 1 and 1.5 g of ceftazidime were stored at 25 °C for 12 hours and then at 37 °C for 14 hours. An aliquot was withdrawn at predefined time points and analyzed for the concentrations of ceftazidime and pyridine.FindingsThe amount of pyridine generated was >225% and 400% of its maximum recommended daily exposure in the 1- and 1.5-g ceftazidime-PD admixtures, respectively.ImplicationsUntil these results are confirmed with appropriate in vivo studies, intermittent intraperitoneal dosing of ceftazidime admixed with icodextrin should be used with caution and appropriate clinical monitoring or a suitable alternative antibiotic should be used.     

The 2009 North Water anomaly

The North Water (NOW) polynya is an area of ocean between Greenland and Ellesmere Island that does not freeze completely during the winter months. The northern border of the polynya is typically demarked by an ice arch that forms across the narrow head of Smith Sound during winter. Once the ice arch consolidates, winds and current advect ice to the south, allowing the formation of new ice. The ice arch generally breaks down in late spring, at which point floes enter the region from the Arctic Ocean via Nares Strait. In 2009, the Smith Sound ice arch did not consolidate, but another ice arch formed 500 km to the north at the junction of Nares Strait and the Arctic Ocean. This northern ice arch prevented floes from reaching the NOW until 23 July and led to decadal low ice coverage for the region. In July, satellite-derived sea surface temperatures (SSTs) reached 8–10°C, which is approximately 5°C above typical seasonal values. With the introduction of floes into the NOW after 23 July, SSTs began to moderate.