scholarly journals The impact of both a priori information and channel estimation errors on the MAP equalizer performance

2006 ◽  
Vol 54 (7) ◽  
pp. 2716-2724 ◽  
Author(s):  
N. Sellami ◽  
A. Roumy ◽  
I. Fijalkow
Keyword(s):  
Channel Estimation ◽  
A Priori ◽  
A Priori Information ◽  
Estimation Errors ◽  
Channel Estimation Errors ◽  
Priori Information ◽  
The Impact

scholarly journals Synergy of stereo cloud top height and ORAC optimal estimation cloud retrieval: evaluation and application to AATSR

2016 ◽  
Vol 9 (3) ◽  
pp. 909-928 ◽  
Author(s):  
Daniel Fisher ◽  
Caroline A. Poulsen ◽  
Gareth E. Thomas ◽  
Jan-Peter Muller
Keyword(s):  
A Priori ◽  
Single Layer ◽  
Optimal Estimation ◽  
Open Water ◽  
A Priori Information ◽  
Cloud Parameters ◽  
Cloud Properties ◽  
Priori Information ◽  
Cloud Parameter ◽  
The Impact

Abstract. In this paper we evaluate the impact on the cloud parameter retrievals of the ORAC (Optimal Retrieval of Aerosol and Cloud) algorithm following the inclusion of stereo-derived cloud top heights as a priori information. This is performed in a mathematically rigorous way using the ORAC optimal estimation retrieval framework, which includes the facility to use such independent a priori information. Key to the use of a priori information is a characterisation of their associated uncertainty. This paper demonstrates the improvements that are possible using this approach and also considers their impact on the microphysical cloud parameters retrieved. The Along-Track Scanning Radiometer (AATSR) instrument has two views and three thermal channels, so it is well placed to demonstrate the synergy of the two techniques. The stereo retrieval is able to improve the accuracy of the retrieved cloud top height when compared to collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), particularly in the presence of boundary layer inversions and high clouds. The impact of the stereo a priori information on the microphysical cloud properties of cloud optical thickness (COT) and effective radius (RE) was evaluated and generally found to be very small for single-layer clouds conditions over open water (mean RE differences of 2.2 (±5.9) microns and mean COD differences of 0.5 (±1.8) for single-layer ice clouds over open water at elevations of above 9 km, which are most strongly affected by the inclusion of the a priori).

scholarly journals Synergy of stereo cloud top height and ORAC optimal estimation cloud retrieval: evaluation and application to AATSR

2015 ◽  
Vol 8 (5) ◽  
pp. 5283-5327
Author(s):  
D. Fisher ◽  
C. A. Poulsen ◽  
G. E. Thomas ◽  
J.-P. Muller
Keyword(s):  
Cloud Model ◽  
A Priori ◽  
Single Layer ◽  
Optimal Estimation ◽  
A Priori Information ◽  
Cloud Parameters ◽  
Microphysical Properties ◽  
Priori Information ◽  
The Impact ◽  
High Clouds

Abstract. In this paper we evaluate the retrievals of cloud top height when stereo derived heights are combined with the radiometric cloud top heights retrieved from the ORAC (Optimal Retrieval of Aerosol and Cloud) algorithm. This is performed in a mathematically rigorous way using the ORAC optimal estimation retrieval framework, which includes the facility to use independent a priori information. Key to the use of a priori information is a characterisation of their associated uncertainty. This paper demonstrates the improvements that are possible using this approach and also considers their impact on the microphysical cloud parameters retrieved. The AATSR instrument has two views and three thermal channels so is well placed to demonstrate the synergy of the two techniques. The stereo retrieval is able to improve the accuracy of the retrieved cloud top height when compared to collocated Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), particularly in the presence of boundary layer inversions and high clouds. The impact on the microphysical properties of the cloud such as optical depth and effective radius was evaluated and found to be very small with the biggest differences occurring over bright land surfaces and for high clouds. Overall the cost of the retrievals increased indicating a poorer radiative fit of radiances to the cloud model, which currently uses a single layer cloud model. Best results and improved fit to the radiances may be obtained in the future if a multi-layer model is used.

scholarly journals The Impact of Transiting Planet Science on the Next Generation of Direct-Imaging Planet Searches

2008 ◽  
Vol 4 (S253) ◽  
pp. 556-559
Author(s):  
Joseph C. Carson
Keyword(s):  
A Priori ◽  
Major Axis ◽  
Next Generation ◽  
A Priori Information ◽  
Direct Imaging ◽  
Semi Major Axis ◽  
Absorption Bands ◽  
Imaging Results ◽  
Priori Information ◽  
The Impact

AbstractWithin the next five years, a number of direct-imaging planet search instruments, like the VLT SPHERE instrument, will be coming online. To successfully carry out their programs, these instruments will rely heavily on a-priori information on planet composition, atmosphere, and evolution. Transiting planet surveys, while covering a different semi-major axis regime, have the potential to provide critical foundations for these next-generation surveys. For example, improved information on planetary evolutionary tracks may significantly impact the insights that can be drawn from direct-imaging statistical data. Other high-impact results from transiting planet science include information on mass-to-radius relationships as well as atmospheric absorption bands. The marriage of transiting planet and direct-imaging results may eventually give us the first complete picture of planet migration, multiplicity, and general evolution.

A Practical Filter for Systems With Unknown Parameters

1973 ◽  
Vol 95 (4) ◽  
pp. 396-401 ◽  
Author(s):  
T. Soeda ◽  
T. Yoshimura
Keyword(s):  
Dynamic Systems ◽  
Digital Simulation ◽  
A Priori ◽  
A Priori Information ◽  
Unknown Parameters ◽  
Estimation Errors ◽  
Time Dynamic ◽  
Filter Performance ◽  
Modeling Errors ◽  
Priori Information

This paper deals with the problem of a practical filter for discrete-time, dynamic systems with unknown parameters whose variation cannot be estimated in advance. The modeling errors caused by unknown parameters clearly degrade the filter performance and sometimes lead to divergence of estimation errors. Divergence is said to occur when the calculated covariance of estimation errors becomes very small comparing with the actual covariance. A practical filter that modifies the calculated covariance is developed as a technique for controlling the divergence. This is done by testing whether or not the actual residual at each stage is likely to have come from the calculated distribution, and the calculated covariance is modified when the test is rejected. The numerical results of digital simulation indicate that divergence of estimation errors is observed when the a priori information for dynamic systems is in error and that the divergence is prevented by the proposed filter.

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