85 research outputs found
Recommended from our members
AIRS/AMSU/HSB validation
No full textThe Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit/Humidity Sounder for Brazil (AIRS/AMSU/HSB) instrument suite onboard Aqua observes infrared and microwave radiances twice daily over most of the planet. AIRS offers unprecedented radiometric accuracy and signal to noise throughout the thermal infrared. Observations from the combined suite of AIRS, AMSU, and HSB are processed into retrievals of atmospheric parameters such as temperature, water vapor, and trace gases under all but the cloudiest conditions. A more limited retrieval set based on the microwave radiances is obtained under heavy cloud cover. Before measurements and retrievals from AIRS/AMSU/HSB instruments can be fully utilized they must be compared with the best possible in situ and other ancillary "truth" observations. Validation is the process of estimating the measurement and retrieval uncertainties through comparison with a set of correlative data of known uncertainties. The ultimate goal of the validation effort is retrieved product uncertainties constrained to those of radiosondes: tropospheric rms uncertainties of 1.0 degC over a 1-km layer for temperature, and 10% over 2-km layers for water vapor. This paper describes the data sources and approaches to be used for validation of the AIRS/AMSU/HSB instrument suite, including validation of the forward models necessary for calculating observed radiances, validation of the observed radiances themselves, and validation of products retrieved from the observed radiances. Constraint of the AIRS product uncertainties to within the claimed specification of 1 K/1 km over well-instrumented regions is feasible within 12 months of launch, but global validation of all AIRS/AMSU/HSB products may require considerably more time due to the novelty and complexity of this dataset and the sparsity of some types of correlative observations
Comparison between MODIS and AIRS/AMSU satellite-derived surface skin temperatures
No full textSurface skin temperatures of the Level 3 products of MODIS Collection 5 (C5) and AIRS/AMSU version 5 (V5) have been compared in terms of monthly anomaly trends and climatologies over the globe during the period from September 2002 to August 2011. The MODIS temperatures in the 50° N-50° S region tend to systematically be ∼1.7 K colder over land and ∼0.5 K warmer over ocean than the AIRS/AMSU temperatures. Over high latitude ocean the MODIS sea surface temperature (SST) values are ∼5.5 K warmer than the AIRS/AMSU. The discrepancies between the annual averages of the two sensors are as much as ∼12 K in the sea ice regions. Meanwhile, the MODIS ice surface temperature product (MYD29E1D) over the ocean is in better agreement with AIRS/AMSU temperatures, showing a root mean square error of 3.7-3.9 K. The disagreement between the two sensors results mainly from the differences in ice/snow emissivity between MODIS infrared and AMSU microwave, and also in their observational local times. Both MODIS and AIRS/AMSU show cooling rates from -0.05±0.06 to -0.14±0.07 K 9 yr-1 over the globe, but warming rates (0.02±0.12 -0.15±0.19 K 9 yr-1) in the high latitude regions. © Author(s) 2013. CC Attribution 3.0 License
Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds
No full textThe first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle- and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables. Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (Vmax). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1–10 Tb data (δrTb), the squares of these gradients, a channel-15-based scattering index (SI89), and area-averaged Tb. Calculations of Tb and δrTb from mesoscale model simulations of Andrew (1992) reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center Vmax estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of Vmax, the average error standard deviation was 4.7 m s−1. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m s−1. Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.
Corresponding author address: Roy W. Spencer, NASA Marshall Space Flight Center, Global Hydrology and Climate Center, 320 Sparkman Drive, Huntsville, AL 35805
A practical demonstration on AMSU retrieval precision for upper tropospheric humidity by a non-linear multi-channel regression method
No full textA neural network algorithm inverting selected channels from the Advance Microwave Sounding Unit instruments AMSU-A and AMSU-B was applied to retrieve layer averaged relative humidity. The neural network was trained with a global synthetic dataset representing clear-sky conditions. A precision of around 6% was obtained when retrieving global simulated radiances, the precision deteriorated less than 1% when real mid-latitude AMSU radiances were inverted and compared with co-located data from a radiosonde station. The 6% precision outperforms by 1% the reported precision estimate from a linear single-channel regression between radiance and weighting function averaged relative humidity, the more traditional approach to exploit AMSU data. Added advantages are not only a better precision; the AMSU-B humidity information is more optimally exploited by including temperature information from AMSU-A channels; and the layer averaged humidity is a more physical quantity than the weighted humidity, for comparison with other datasets. The training dataset proved adequate for inverting real radiances from a mid-latitude site, but it is limited by not considering the impact of clouds or surface emissivity changes, and further work is needed in this direction for further validation of the precision estimates
The impact of ozone lines on AMSU-B radiances
No full textThe impact of ozone lines on Advanced Microwave Sounding Unit-B (AMSU-B) radiances was investigated using a line-by-line radiative transfer model. The impact is found to be the largest for channel 18 (183.31 ± 1.00 GHz), with a maximum up to about 0.5 K. The channels 17 (150 GHz) and 20 (183.31 ± 7.00 GHz) are also marginally affected by the ozone lines. The magnitude of the impact shows an interesting dependence on the channel 18 brightness temperature which implies that the effect is not just an offset to the brightness temperature.Upprättat; 2004; 20070502 (pafi
Retrieval of upper tropospheric water vapor and upper tropospheric humidity from AMSU radiances
No full textA regression method was developed to retrieve upper tropospheric water vapor (UTWV in kg/m2) and upper tropospheric humidity (UTH in % RH) from radiances measured by the Advanced Microwave Sounding Unit (AMSU). In contrast to other UTH retrieval methods, UTH is defined as the average relative humidity between 500 and 200hPa, not as a Jacobian weighted average, which has the advantage that the UTH altitude does not depend on the atmospheric conditions. The method uses AMSU channels 6-10, 18, and 19, and should achieve an accuracy of 0.48 kg/m2 for UTWV and 6.3% RH for UTH, according to a test against an independent synthetic data set. This performance was confirmed for northern mid-latitudes by a comparison against radiosonde data from station Lindenberg in Germany, which yielded errors of 0.23 kg/m2 for UTWV and 6.1% RH for UTH
Scan asymmetries in AMSU-B data
No full textA simple method of averaging measurements for different scan positions was used to quantify scan asymmetries in AMSU-B brightness temperatures for the sensors on the satellites NOAA 15, 16, and 17. The method works particularly well for the sounding channels 18 to 20. The asymmetries are small in most cases. In particular, asymmetries for Channel 18 are below 1.90, −0.53, and 0.49 K for NOAA 15, 16, and 17, respectively. On the other hand, it was found that the instrument on NOAA 15 has significant asymmetries for Channels 19 and 20, which seem to be related to the known radio frequency interference problem for this instrument. The use of the appropriate set of interference correction coefficients significantly reduces the asymmetry.Upprättat; 2005; 20070502 (pafi
Soil moisture variations monitoring by AMSU-based soil wetness indices: A long-term inter-comparison with ground measurements.
No full textSoil moisture controls the partitioning of rainfall into runoff and infiltration and, consequently, the runoff generation. On the catchment scale its routine monitoring can be performed through remote sensing technologies. Within this framework, the purpose of this study is to investigate the potential of the Advanced Microwave Sounding Unit (AMSU), radiometer on board the NOAA (National Oceanic and Atmospheric Administration) satellites and operating since 1998, for the assessment of soil wetness conditions by comparing soil moisture data with both those measured in situ and provided by a continuous rainfall-runoff model applied to four catchments located in the Upper Tiber River (Central Italy). In particular, in order to perform a robust analysis an extensive and long-term period (nine years) of data was investigated. In detail, the Soil Wetness Variation Index, derived from the AMSU data modified in order to take account of the difference between the soil layer investigated by the satellite sensor and that used as a benchmark, was found to be correlated both with the in-situ and modeled soil moisture variations showing correlation coefficients in the range of 0.42-0.49 and 0.33-0.48, respectively. As far as the soil moisture temporal pattern is concerned, higher correlations were obtained (0.59-0.84 for the in-situ data and 0.82-0.87 for the modeled data set) partly due to the soil moisture seasonal pattem that enhances the correlation. Overall, the root mean square error was found to be less than 0.05 m(3)/m(3) for both the comparisons, thus assessing the potential of the AMSU sensor to quantitatively retrieve soil moisture temporal patterns. Moreover. the AMSU sensor can be considered as a useful tool to provide a reliable and frequently updated global soil moisture data set, considering its higher temporal resolution now available (about 4 passes per day) thanks to the presence of the sensor aboard different satellites
Convective activity in Mato Grosso state (Brazil) from microwave satellite observations: Comparisons between AMSU and TRMM datasets
No full textInternational audienceWe present a characterization of convective activity at sub-regional scale from two sets of satellite-based microwave observations: the Advanced Microwave Sounding Unit (AMSU) and the combined Tropical Rainfall Measuring Mission (TRMM) microwave imager and precipitation radar data, for the period 2001 to 2011. We focus on the state of Mato Grosso, Brazil, located at the southern edge of the so-called "Legal Amazon" which has undergone intense land cover transformation in the last 4 decades. The annual cycle of mean convective activity described by AMSU and TRMM are in good agreement, with a correlation close to 0.80. The mean amplitude of convective activity is maximal early in the rainy season, except for AMSU deep convective area, which presents a maximum in January. The diurnal cycle of convection was examined for the period 2003 to 2007, and it was found that convection is maximal near 1500 local time (LT) and minimal around 0700 LT. Unlike the amplitude, the phase shows little intra-seasonal and interannual variability. A slight decrease in convective activity in the studied period was found possibly indicating an extension of the dry season. Comparisons of convective activity between deforested and forested areas showed no significant differences in the phase of the diurnal cycle, but our analysis shows a tendency for increase (decrease) in convection in deforested (forested) areas for the period considered. A longer time series is however necessary in order to strengthen the robustness of our results
Dietetics and other dietary patterns of the Karisal region in Natar literature
No full textTamil has always lived in harmony with nature. So his life also went smoothly without complications. Conflicts can be avoided if you know the time and place and live naturally. Their food types were also based on that and they used the food plants available in nature as food and that is why they were used as food and medicine. That is why the old saying that food is medicine is medicine
- …
