scholarly journals Spectral Bias Estimation of Historical HIRS Using IASI Observations for Improved Fundamental Climate Data Records

2009 ◽  
Vol 26 (7) ◽  
pp. 1378-1387 ◽  
Author(s):  
Changyong Cao ◽  
Mitch Goldberg ◽  
Likun Wang
Keyword(s):  
Measurement Errors ◽  
International System ◽  
Spectral Response ◽  
Observation Time ◽  
Lapse Rate ◽  
Polar Regions ◽  
Bias Estimation ◽  
Climate Data ◽  
Infrared Observation ◽  
System Of Units

Abstract A prerequisite for climate change detection from satellites is that the measurements from a series of historical satellites must be consistent and ideally made traceable to the International System of Units (SI). Unfortunately, this requirement is not met for the 14 High Resolution Infrared Radiation Sounders (HIRS) on the historical NOAA satellites, because the instrument was developed for weather forecasts and lacks accuracy and consistency across satellites. It is well known that for HIRS, differences in the spectral response functions (SRF) between instruments and their prelaunch measurement uncertainties often lead to observations of the atmosphere at different altitudes. As a result of the atmospheric lapse rate, they both can introduce significant intersatellite biases. The SRF-dependent biases are further mixed with other effects such as the diurnal cycle because of observation time differences and orbital drifts, on board calibration, and algorithm issues. In this study, the Infrared Atmospheric Sounding Interferometer (IASI) observations are used to calculate the radiances for the 14 Television Infrared Observation Satellite series N (TIROS-N; to MetOp-A) HIRS instruments in different climate regimes and seasons to separate the SRF-induced intersatellite biases from other factors. It is found that the calculated radiance ratio (a bias indicator) using IASI observations for the HIRS satellite pairs forms bell-shaped curves that vary with the HIRS model and channel as well as climate regimes. This suggests that a bias found in the polar regions at the Simultaneous Nadir Overpass (SNO) cannot be blindly used for bias correction globally; instead, the IASI/HIRS spectral bias bell curves should be used as a complement to more fully address the biases. These bell curves also serve as lookup charts for separating the bias due to true SRF differences from that caused by SRF prelaunch measurement errors to resolve the inconsistency, which sheds new light on reprocessing and reanalysis in generating fundamental climate data records from HIRS.

Ultracold atoms and precise time standards

2011 ◽  
Vol 369 (1953) ◽  
pp. 4078-4089 ◽  
Author(s):  
Gretchen K. Campbell ◽  
William D. Phillips
Keyword(s):  
Laser Cooling ◽  
International System ◽  
Microwave Frequency ◽  
Observation Time ◽  
Mass Motion ◽  
Frequency Standards ◽  
Systematic Uncertainties ◽  
System Of Units ◽  
Time Standards ◽  
Atomic Frequency

Experimental techniques of laser cooling and trapping, along with other cooling techniques, have produced gaseous samples of atoms so cold that they are, for many practical purposes, in the quantum ground state of their centre-of-mass motion. Such low velocities have virtually eliminated effects such as Doppler shifts, relativistic time dilation and observation-time broadening that previously limited the performance of atomic frequency standards. Today, the best laser-cooled, caesium atomic fountain, microwave frequency standards realize the International System of Units (SI) definition of the second to a relative accuracy of ≈3×10 −16 . Optical frequency standards, which do not realize the SI second, have even better performance: cold neutral atoms trapped in optical lattices now yield relative systematic uncertainties of ≈1×10 −16 , whereas cold-trapped ions have systematic uncertainties of 9×10 −18 . We will discuss the current limitations in the performance of neutral atom atomic frequency standards and prospects for the future.

scholarly journals Intersatellite Radiance Biases for the High-Resolution Infrared Radiation Sounders (HIRS) on board NOAA-15, -16, and -17 from Simultaneous Nadir Observations

2005 ◽  
Vol 22 (4) ◽  
pp. 381-395 ◽  
Author(s):  
Changyong Cao ◽  
Hui Xu ◽  
Jerry Sullivan ◽  
Larry McMillin ◽  
Pubu Ciren ◽  
...  
Keyword(s):  
High Resolution ◽  
Infrared Radiation ◽  
Spectral Response ◽  
Lapse Rate ◽  
Polar Regions ◽  
Spatial Uniformity ◽  
Accuracy And Precision ◽  
Instrument Noise ◽  
Highly Correlated

Abstract Intersatellite radiance comparisons for the 19 infrared channels of the High-Resolution Infrared Radiation Sounders (HIRS) on board NOAA-15, -16, and -17 are performed with simultaneous nadir observations at the orbital intersections of the satellites in the polar regions, where each pair of the HIRS views the same earth target within a few seconds. Analysis of such datasets from 2000 to 2003 reveals unambiguous intersatellite radiance differences as well as calibration anomalies. The results show that in general, the intersatellite relative biases are less than 0.5 K for most HIRS channels. The large biases in different channels differ in both magnitude and sign, and are likely to be caused by the differences and measurement uncertainties in the HIRS spectral response functions. The seasonal bias variation in the stratosphere channels is found to be highly correlated with the lapse rate factor approximated by the channel radiance differences. The method presented in this study works particularly well for channels sensing the stratosphere because of the relative spatial uniformity and stability of the stratosphere, for which the intercalibration accuracy and precision are mostly limited by the instrument noise. This method is simple and robust, and the results are highly repeatable and unambiguous. Intersatellite radiance calibration with this method is very useful for the on-orbit verification and monitoring of instrument performance, and is potentially useful for constructing long-term time series for climate studies.

Dimensions of plane and solid angles and their units in the International System of Units (SI)

2020 ◽  
pp. 26-32
Author(s):  
M. I. Kalinin ◽  
L. K. Isaev ◽  
F. V. Bulygin
Keyword(s):  
Solid Angle ◽  
International System ◽  
International Committee ◽  
Plane Angle ◽  
Arc Length ◽  
Weights And Measures ◽  
International System Of Units ◽  
System Of Units ◽  
In Series ◽  
Solid Angles

The situation that has developed in the International System of Units (SI) as a result of adopting the recommendation of the International Committee of Weights and Measures (CIPM) in 1980, which proposed to consider plane and solid angles as dimensionless derived quantities, is analyzed. It is shown that the basis for such a solution was a misunderstanding of the mathematical formula relating the arc length of a circle with its radius and corresponding central angle, as well as of the expansions of trigonometric functions in series. From the analysis presented in the article, it follows that a plane angle does not depend on any of the SI quantities and should be assigned to the base quantities, and its unit, the radian, should be added to the base SI units. A solid angle, in this case, turns out to be a derived quantity of a plane angle. Its unit, the steradian, is a coherent derived unit equal to the square radian.

scholarly journals A quantum ampere

2020 ◽  
Vol 87 (4) ◽  
pp. 258-265
Author(s):  
Luca Callegaro
Keyword(s):  
Electric Current ◽  
International System ◽  
International System Of Units ◽  
System Of Units ◽  
Elementary Charge ◽  
User Friendly

AbstractThe revision of the International System of Units (SI), implemented since 20 May 2019, has redefined the unit of electric current, the ampere ( A), linking it to a fixed value of the elementary charge. This paper discusses the new definition and the realisation of the electrical units by quantum electrical metrology standards, which every year become more and more accessible, reliable and user friendly.

SI, the international system of units

1973 ◽  
Vol 1 (2) ◽  
pp. 217-241 ◽  
Author(s):  
Wm. Markowitz
Keyword(s):  
International System ◽  
International System Of Units ◽  
System Of Units

Investigation on the Noise Separation in Watt Balance Experiments

2008 ◽  
Vol 381-382 ◽  
pp. 619-622
Author(s):  
W. Zeng ◽  
Xiang Qian Jiang ◽  
P. Scott ◽  
L. Blunt
Keyword(s):  
Background Noise ◽  
International System ◽  
Histogram Method ◽  
Stationary Noise ◽  
Vibration Data ◽  
System Of Units ◽  
Environmental Vibration ◽  
Transient Events ◽  
Watt Balance ◽  
Definition Of

The detection of stationary and non-stationary noise in environmental vibration data is an important issue when considering the precision of the Watt balance, an electromechanical apparatus for the new definition of the kilogram in the international system of Units (SI). In this paper, the authors propose a frequency histogram method to find the structure of the stationary noise from large amount of datasets. For the non-stationary noise, the authors propose a wavelet based denoising methods to distinguish the transient events from the background “noise”, to find their duration and content and to identify their location in time.

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