A heterogeneous catalyst, nanosized MCM-41-Pd, was used to catalyze the Sonogashira coupling of aryl and heteroaryl halides with terminal alkynes in the presence of CuI and triphenylphosphine. The coupling products were obtained in high yields using low Pd loadings to 0.01 mol%, and the nanosized MCM-41-Pd catalyst was recovered by centrifugation of the reaction solution and re-used in further runs without significant loss of reactivity.

Sonogashira Reaction of Aryl and Heteroaryl Halides with Terminal Alkynes Catalyzed by a Highly Efficient and Recyclable Nanosized MCM-41 Anchored Palladium Bipyridyl Complex

The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Ocean and Sea Ice Satellite Application Facility (OSI SAF) produces near-real-time scatterometer ocean vector winds since almost 20 years already. Data from the European remote sensing satellites (ERS-1 and ERS-2 scatterometer), QuikSCAT (SeaWinds), Metop (ASCAT), Oceansat 2 (OSCAT), and RapidScat on the International Space Station have been, or are being, produced. The OSI SAF scatterometer products, produced at the Royal Netherlands Meteorological Institute, provide superior comparison to both buoy and numerical weather prediction (NWP) datasets. Moreover, the wind processing software is publicly available through the EUMETSAT NWP SAF. An increasing amount of users employs scatterometer wind data for climate studies. However, the wind retrieval algorithms have been continuously improved over the years and the currently existing archives of near-real-time data are not always suitable to fulfill the need for homogeneous datasets spanning a longer period of time. Currently, only few validated vector wind climate datasets are available. Therefore, the OSI SAF is reprocessing several offline datasets. This paper is focusing on two climate data records from SeaWinds and ASCAT winds, which together span the period from 1999 to 2014. The data are compared to the NWP model and buoy winds. The stability of the wind characteristics is assessed and an attempt is made to attribute temporal changes to climatological and NWP model changes over time.

Long-Term Scatterometer Wind Climate Data Records

Uncertainties in the retrievals of microwave land-surface emissivities are quantified over two types of land surfaces: desert and tropical rainforest. Retrievals from satellite-based microwave imagers, including the Special Sensor Microwave Imager, the Tropical Rainfall Measuring Mission Microwave Imager, and the Advanced Microwave Scanning Radiometer for Earth Observing System, are studied. Our results show that there are considerable differences between the retrievals from different sensors and from different groups over these two land-surface types. In addition, the mean emissivity values show different spectral behavior across the frequencies. With the true emissivity assumed largely constant over both of the two sites throughout the study period, the differences are largely attributed to the systematic and random errors in the retrievals. Generally, these retrievals tend to agree better at lower frequencies than at higher ones, with systematic differences ranging 1%-4% (3-12 K) over desert and 1%-7% (3-20 K) over rainforest. The random errors within each retrieval dataset are in the range of 0.5%-2% (2-6 K). In particular, at 85.5/89.0 GHz, there are very large differences between the different retrieval datasets, and within each retrieval dataset itself. Further investigation reveals that these differences are most likely caused by rain/cloud contamination, which can lead to random errors up to 10-17 K under the most severe conditions.

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Quantifying Uncertainties in Land-Surface Microwave Emissivity Retrievals

The accuracy of ocean surface wind vectors measured by satellite-borne scatterometers depends on measured backscattering coefficient (σ°). Hence, an in-flight calibration of a satellite scatterometer is essential as this is not guaranteed by its prelaunch absolute calibration. The postlaunch calibration of σ° is also required to monitor the time evolution of the accuracy of measured σ °. This is performed using relative calibration over land targets with minor spatiotemporal variation of σ°. A few such targets are the Amazon rainforest, Greenland, Antarctica, etc. In this paper, relative calibration of σ° from the OceanSAT-2 Scatterometer (OSCAT) has been carried out by comparing it with a similar quantity from the Quick Scatterometer (QuikSCAT) for November 2009. The differences between the average σ° of QuikSCAT and that of OSCAT have been calculated globally to check the overall consistency. Over the calibration sites, the differences are within ±0.25 dB. Histograms of differences in ascending/descending passes and fore/aft looks of OSCAT have also been analyzed over the calibration sites. These indicate that look bias in OSCAT σ° is within the range of ±0.5 dB. It is also evident that pass biases, i.e., differences between ascending and descending passes, exist over the Amazon rainforest for both QuikSCAT and OSCAT. This diurnal variation in σ° may go up to 1.25 dB in OSCAT. Further, computations of daily average and standard deviation over the calibration site show that mean OSCAT σ° is consistent with mean QuikSCAT σ°, whereas the standard deviation in OSCAT is marginally higher. Further, time-series analysis of OSCAT σ° shows its temporal stability.

Cross Calibration of the OceanSAT -2 Scatterometer With QuikSCAT Scatterometer Using Natural Terrestrial Targets

Launched in September2014, RapidScat is currently operating on the International Space Station (ISS). RapidScat estimates ocean vector winds via the measurement of the normalized radar coefficient (σ
 0
) of the ocean's surface. Measurements are also collected over land. The ISS orbit permits, for the first time, the observation of the diurnal variation in Ku-band σ
 0
 at midto high-incidence angles. To complement calibration efforts over the ocean, in this paper the calibration and validation of the σ
 0
 measurements are performed using natural land targets, namely the Amazon and Congo rainforests. The diurnal σ
 0
 cycle of the targets is estimated with respect to incidence angle, azimuth angle, and season using measurements from previous sensors. Understanding this diurnal backscatter response enables the comparison of RapidScat measurements with measurements from the QuikSCAT, NASA Scatterometer, SeaWinds, and Oceansat-II scatterometers. RapidScat σ
 0
 measurements are found to be consistent but biased low compared to those of QuikSCAT by up to 0.3 dB. The effectiveness of slice balancing is evaluated and found to be dependent on the pitch of the ISS. Extreme pitches of the ISS are also found to introduce azimuth dependencies in egg measurements. By accounting for seasonal and diurnal cycles, we find that the rainforests are well suited for scatterometer sensor cross-calibration, even for disjoint years.

Calibration and Validation of the RapidScat Scatterometer Using Tropical Rainforests

Scatterometer instruments transmit a series of microwave pulses and measure the returned echo to determine the normalized radar cross section (σ0) over the target to derive the near-ocean-surface wind vector. Accuracy of the derived wind vector over the data sparse oceans therefore depends on the accuracy of σ0 measurement. For this purpose, accurate calibration of the scatterometer is required. As a preparation toward calibration of the Oceansat-2 mission, of the Indian Space Research Organisation, a relative calibration technique has been proposed in this study by selecting homogeneous areas over the globe with isotropic radar response and temporally stable signature of σ0. For this purpose, the daily averaged σ0 and Level-2A (L2A) σ0 measurements of the QuikSCAT scatterometer have been used. Analyzing the monthly mean and standard deviation in σ0 for the period of 2005-2006, several regions are chosen which have a quasi-isotropic radar response and minimal temporal variation in σ0. The analysis shows that the selected areas over Antarctica and Greenland with permanent ice covers have temporally stable signatures of σ0. The regions like the Amazon forests and parts of Australia also show high temporal stability of σ0 but greater standard deviation than the snow-covered areas. The QuikSCAT L2A data have also been used to study the day-night variation and azimuthal dependence of the σ0 over these targets. The present work demonstrated that quasi-uniform natural sites such as Sahara, Amazon forest, Kutch, Greenland region, and Antarctica region, covering wide dynamic range of σ0, can be used for the purpose of calibration.

Relative Calibration Using Natural Terrestrial Targets: A Preparation Towards Oceansat-2 Scatterometer

A convenient method for the preparation of thienylacetylnes

Spaceborne radar scatterometers operating in microwave frequency bands have several science and operational applications in Oceanography, meteorology, agricultural and geophysical sciences. The basic parameter measured by a scatterometer is the Backscattering coefficient (p^0) for a certain frequency, polarization and observational geometry. Before addressing a specific application, it is needed that the p^0 signatures be analyzed over natural, undisturbed and uniform/quasi-uniform target areas. As a prelude to ISRO's forthcoming OceanSat-II mission, carrying a Ku-band scatterometer, QuikSCAT scatterometer measured p^0 data are analyzed over its dynamical range using the global natural targets.

K. N. Babu

Papers

Relative Calibration Using Natural Terrestrial Targets: A Preparation Towards Oceansat-2 Scatterometer

A convenient method for the preparation of thienylacetylnes

A study of QuikSCAT measured backscattering coefficient data over global natural targets

A Convenient Method for the Preparation of Thienylacetylenes.