scholarly journals Retrieval of Cloud Liquid Water Using Microwave Signals from LEO Satellites: A Feasibility Study through Simulations

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 460
Author(s):  
Xi Shen ◽  
Defeng David Huang ◽  
Wenxiao Wang ◽  
Andreas F. Prein ◽  
Roberto Togneri
Keyword(s):  
Liquid Water ◽  
Signal To Noise Ratio ◽  
Low Earth Orbit ◽  
Basis Functions ◽  
Retrieval Algorithm ◽  
Cloud Liquid Water ◽  
Novel Approach ◽  
Communication Links ◽  
Gaussian Basis Functions ◽  
Leo Satellite

A novel approach, using low Earth orbit (LEO) satellite microwave communication links for cloud liquid water measurements, is proposed in this paper. The feasibility of this approach is studied through simulations of the retrieval system including a LEO satellite communicating with a group of ground receivers equipped with signal-to-noise ratio (SNR) estimators, a synthetic cloud attenuation field and a tomographic retrieval algorithm. Rectangular and Gaussian basis functions are considered to define the targeted field. Simulation results suggest that the proposed least-squares based retrieval algorithm produces satisfactory outcomes for both types of basis functions. The root-mean-square error of the retrieved field is around 0.2 dB/km, with the range of the reference field as 0 to 2.35 dB/km. It is also confirmed that the partial retrieval of the cloud field is achievable when a limited number of receivers with restricted locations are available. The retrieval outcomes exhibit properties of high resolution and low error, indicating that the proposed approach has great potential for cloud observations.

scholarly journals Retrieval of Raindrop Size Distribution Using Dual-Polarized Microwave Signals from LEO Satellites: A Feasibility Study through Simulations

Sensors ◽  
2021 ◽  
Vol 21 (19) ◽  
pp. 6389
Author(s):  
Xi Shen ◽  
Defeng David Huang
Keyword(s):  
Size Distribution ◽  
Signal To Noise Ratio ◽  
Low Earth Orbit ◽  
Earth Orbit ◽  
Horizontal Polarization ◽  
Novel Approach ◽  
Raindrop Size Distribution ◽  
Microwave Signals ◽  
Dual Polarized ◽  
Raindrop Size

In this paper, a novel approach for raindrop size distribution retrieval using dual-polarized microwave signals from low Earth orbit satellites is proposed. The feasibility of this approach is studied through modelling and simulating the retrieval system which includes multiple ground receivers equipped with signal-to-noise ratio estimators and a low Earth orbit satellite communicating with the receivers using both vertically and horizontally polarized signals. Our analysis suggests that the dual-polarized links offer the opportunity to estimate two independent raindrop size distribution parameters. To achieve that, the vertical and horizontal polarization attenuations need to be measured at low elevation angles where the difference between them is more distinct. Two synthetic rain fields are generated to test the performance of the retrieval. Simulation results suggest that the specific attenuations for both link types can be retrieved through a least-squares algorithm. They also confirm that the specific attenuation ratio of vertically to horizontally polarized signals can be used to retrieve the slope and intercept parameters of raindrop size distribution.

scholarly journals Improved Retrieval of Cloud Liquid Water from CloudSat and MODIS

2016 ◽  
Vol 55 (8) ◽  
pp. 1831-1844 ◽  
Author(s):  
Jussi Leinonen ◽  
Matthew D. Lebsock ◽  
Graeme L. Stephens ◽  
Kentaroh Suzuki
Keyword(s):  
Liquid Water ◽  
Optimal Estimation ◽  
Estimation Algorithm ◽  
Radar Signal ◽  
Retrieval Algorithm ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Cloud Optical Depth ◽  
Cloud Water Content ◽  
Most Significant Change

AbstractA revised version of the CloudSat–MODIS cloud liquid water retrieval algorithm is presented. The new algorithm, which combines measurements of radar reflectivity and cloud optical depth, addresses issues discovered in the current CloudSat–MODIS cloud water content (CWC) product. This current product is shown to be underconstrained by observations and to be too dependent on prior information incorporated into the Bayesian optimal-estimation algorithm. The most significant change made to the algorithm in this study was decreasing the number of independent variables to allow the observations to constrain the retrieved values better. The retrieval was also reformulated for improved compliance with the mathematical assumptions of the optimal-estimation algorithm. To validate the accuracy of the revised algorithm, the path-integrated attenuation (PIA) of the CloudSat radar signal was computed from the algorithm results. These modeled values were compared with independent measurements of the PIA that were obtained using a surface reference technique. This comparison shows that the cloud liquid water retrieved by the algorithm is close to being unbiased. The revised algorithm was also found to be an improvement over the current CloudSat CWC product and, to a lesser degree, the MODIS-derived cloud liquid water path.

scholarly journals Tomographic retrieval of cloud liquid water fields from a single scanning microwave radiometer aboard a moving platform – Part 2: Observation system simulation experiments

2010 ◽  
Vol 10 (14) ◽  
pp. 6699-6709 ◽  
Author(s):  
D. Huang ◽  
A. Gasiewski ◽  
W. Wiscombe
Keyword(s):  
Liquid Water ◽  
System Simulation ◽  
Microwave Radiometer ◽  
Retrieval Algorithm ◽  
Observation System ◽  
Total Variation Regularization ◽  
L1 Norm ◽  
Simulation Experiments ◽  
Cloud Liquid Water ◽  
L2 Norm

Abstract. Part 1 of this research concluded that many conditions of the 2003 Wakasa Bay experiment were not optimal for the purpose of tomographic retrieval. Part 2 (this paper) then aims to find possible improvements to the mobile cloud tomography method using observation system simulation experiments. We demonstrate that the incorporation of the L1 norm total variation regularization in the tomographic retrieval algorithm better reproduces discontinuous structures than the widely used L2 norm Tikhonov regularization. The simulation experiments reveal that a typical ground-based mobile setup substantially outperforms an airborne one because the ground-based setup usually moves slower and has greater contrast in microwave brightness between clouds and the background. It is shown that, as expected, the error in the cloud tomography retrievals increases monotonically with both the radiometer noise level and the uncertainty in the estimate of background brightness temperature. It is also revealed that a lower speed of platform motion or a faster scanning radiometer results in more scan cycles and more overlap between the swaths of successive scan cycles, both of which help to improve the retrieval accuracy. The last factor examined is aircraft height. It is found that the optimal aircraft height is 0.5 to 1.0 km above the cloud top. To summarize, this research demonstrates the feasibility of tomographically retrieving the spatial structure of cloud liquid water using current microwave radiometric technology and provides several general guidelines to improve future field-based studies of cloud tomography.

scholarly journals Cross-comparison of cloud liquid water path derived from observations by two space-borne and one ground-based instrument in northern Europe

2019 ◽  
Vol 12 (11) ◽  
pp. 5927-5946 ◽  
Author(s):  
Vladimir S. Kostsov ◽  
Anke Kniffka ◽  
Martin Stengel ◽  
Dmitry V. Ionov
Keyword(s):  
Liquid Water ◽  
Spatial Inhomogeneity ◽  
Retrieval Algorithm ◽  
Liquid Water Path ◽  
Simple Estimate ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Geographical Regions ◽  
Temporal And Spatial ◽  
Cloud Liquid Water Path

Abstract. Cloud liquid water path (LWP) is one of the target atmospheric parameters retrieved remotely from ground-based and space-borne platforms using different observation methods and processing algorithms. Validation of LWP retrievals is a complicated task since a cloud cover is characterised by strong temporal and spatial variability while remote sensing methods have different temporal and spatial resolutions. An attempt has been made to compare and analyse the collocated LWP data delivered by two satellite instruments SEVIRI and AVHRR together with the data derived from microwave observations by the ground-based radiometer RPG-HATPRO. The geographical region of interest is the vicinity of St. Petersburg, Russia, where the RPG-HATPRO radiometer is operating. The study is focused on two problems. The first one is the so-called scale difference problem, which originates from dissimilar spatial resolutions of measurements. The second problem refers to the land–sea LWP gradient. The radiometric site is located 2.5 km from the coastline where the effects of the LWP gradient are pronounced. A good agreement of data obtained at the microwave radiometer location by all three instruments (HATPRO, SEVIRI, and AVHRR) during warm and cold seasons is demonstrated (the largest correlation coefficient 0.93 was detected for HATPRO and AVHRR datasets). The analysis showed no bias of the SEVIRI results with respect to HATPRO data and a large positive bias (0.013–0.017 kg m−2) of the AVHRR results for both warm and cold seasons. The analysis of LWP maps plotted on the basis of the SEVIRI and AVHRR measurements over land and water surfaces in the vicinity of St. Petersburg revealed the unexpectedly high LWP values delivered by AVHRR during the cold season over the Neva River bay and over the Saimaa Lake and the abnormal land–sea LWP gradient in these areas. For the detailed evaluation of atmospheric state and ice cover in the considered geographical regions during the periods of ground-based and satellite measurements, reanalysis data were used. It is shown that the most probable reason for the observed artefacts in the AVHRR measurements over water and ice surfaces is the coarse resolution of the land–sea and snow–ice masks used by the AVHRR retrieval algorithm. The influence of a cloud field inhomogeneity on the agreement between the satellite and the ground-based data is studied. For this purpose, the simple estimate of the LWP temporal variability is used as a measure of the spatial inhomogeneity. It has been demonstrated that both instruments are equally sensitive to the inhomogeneity of a cloud field despite the fact that they have different spatial resolutions.

On the Consequences of Resampling Microwave Radiometer Observations for Use in Retrieval Algorithms

2009 ◽  
Vol 48 (9) ◽  
pp. 1981-1993 ◽  
Author(s):  
Anita D. Rapp ◽  
M. Lebsock ◽  
C. Kummerow
Keyword(s):  
Wind Speed ◽  
Liquid Water ◽  
Microwave Radiometer ◽  
Retrieval Algorithm ◽  
Time Averaging ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Brightness Temperatures ◽  
Cloud Liquid Water Path

Abstract How to deal with the different spatial resolutions of multifrequency satellite microwave radiometer measurements is a common problem in retrievals of cloud properties and rainfall. Data convolution and deconvolution is a common approach to resampling the measurements to a single resolution. Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements are resampled to the resolution of the 19-GHz field of view for use in a multifrequency optimal estimation retrieval algorithm of cloud liquid water path, total precipitable water, and wind speed. Resampling the TMI measurements is found to have a strong influence on retrievals of cloud liquid water path and a slight influence on wind speed. Beam-filling effects in the resampled brightness temperatures are shown to be responsible for the large differences between the retrievals using the TMI native resolution and resampled brightness temperatures. Synthetic retrievals are performed to test the sensitivity of the retrieved parameters to beam-filling effects in the resampling of each of the different channels. Beam-filling effects due to the convolution of the 85-GHz channels are shown to be the largest contributor to differences in retrieved cloud liquid water path. Differences in retrieved wind speeds are found to be a combination of effects from deconvolving the 10-GHz brightness temperatures and compensation effects due to the lower liquid water path being retrieved by the high-frequency channels. The influence of beam-filling effects on daily and monthly averages of cloud liquid water path is also explored. Results show that space–time averaging of cloud liquid water path cannot fully compensate for the beam-filling effects and should be considered when using cloud liquid water path data for validation or in climate studies.

scholarly journals Cross-comparison of cloud liquid water path derived from observations by two space-borne and one ground-based instrument in Northern Europe

2019 ◽  
Author(s):  
Vladimir S. Kostsov ◽  
Anke Kniffka ◽  
Martin Stengel ◽  
Dmitry V. Ionov
Keyword(s):  
Spatial Resolution ◽  
Liquid Water ◽  
Retrieval Algorithm ◽  
Liquid Water Path ◽  
Simple Estimate ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Geographical Regions ◽  
Temporal And Spatial ◽  
Cloud Liquid Water Path

Abstract. Cloud liquid water path (LWP) is one of the target atmospheric parameters retrieved remotely from ground-based and space-borne platforms using different observation methods and processing algorithms. Validation of LWP retrievals is a complicated task since a cloud cover is characterised by strong temporal and spatial variability while remote sensing methods have different temporal and spatial resolution. An attempt has been made to compare and analyse the collocated LWP data delivered by two satellite instruments SEVIRI and AVHRR together with the data derived from microwave observations by the ground-based radiometer RPG‑HATPRO. The geographical region of interest is the vicinity of St.Petersburg, Russia, where the RPG‑HATPRO radiometer is operating. The study is focused on two problems. The first one is the so-called scale difference problem which originates from dissimilar spatial resolutions of measurements. The second problem refers to the land-sea LWP gradient. The radiometric site is located 2.5 km from the coastline where the effects of the LWP gradient are pronounced. A good agreement of data obtained at the microwave radiometer location by all three instruments (HATPRO, SEVIRI and AVHRR) during warm and cold seasons is demonstrated (the largest correlation coefficient 0.93 was detected for HATPRO and AVHRR data sets). The analysis showed no bias of the SEVIRI results with respect to HATPRO data and a high bias (0.013–0.017 kg m−2) of the AVHRR results for both warm and cold seasons. The analysis of LWP maps plotted on the basis of the SEVIRI and AVHRR measurements over land and water surfaces in the vicinity of St.Petersburg revealed the unexpectedly high LWP values delivered by AVHRR during cold season over the Neva river bay and over the Saimaa Lake and the abnormal land-sea LWP gradient in these areas. For the detailed evaluation of atmospheric state and ice cover in the considered geographical regions during the periods of ground-based and satellite measurements, reanalysis data were used. It is shown that the most probable reason for the observed artifacts in the AVHRR measurements over water/ice surfaces is the coarse resolution of the land-sea and snow/ice masks used by the AVHRR retrieval algorithm. The influence of a cloud field inhomogeneity on the agreement between the satellite and the ground-based data was studied. For this purpose, the simple estimate of the LWP temporal variability was used as a measure of the spatial inhomogeneity. It has been demonstrated that both instruments are equally sensitive to the inhomogeneity of a cloud field despite the fact that they have different spatial resolution.

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