scholarly journals Preliminary Evaluation and Correction of Sea Surface Height from Chinese Tiangong-2 Interferometric Imaging Radar Altimeter

2020 ◽  
Vol 12 (15) ◽  
pp. 2496
Author(s):  
Lin Ren ◽  
Jingsong Yang ◽  
Xiao Dong ◽  
Yunhua Zhang ◽  
Yongjun Jia
Keyword(s):  
Sea Surface Height ◽  
Sea Surface ◽  
Retrieval Algorithm ◽  
Preliminary Evaluation ◽  
Interferometric Imaging ◽  
Radar Altimeter ◽  
Sea State ◽  
Imaging Radar ◽  
Sea State Bias ◽  
Wide Swath

In this study, we performed preliminary comparative evaluation and correction of two-dimensional sea surface height (SSH) data from the Chinese Tiangong-2 Interferometric Imaging Radar Altimeter (InIRA) with the goal of advancing its retrieval. Data from the InIRA were compared with one-dimensional SSH data from the traditional altimeters Jason-2, Saral/AltiKa, and Jason-3. Because the sea state bias (SSB) of distributed InIRA data has not yet been considered, consistency was maintained by neglecting the SSB for the traditional altimeters. The results of the comparisons show that the InIRA captures the same SSH trends as those obtained by traditional altimeters. However, there is a significant deviation between InIRA and traditional altimeter SSHs; consequently, systematic and parametric biases were analyzed. The parametric bias was found to be related to the incidence angles and a significant wave height. Upon correcting the two biases, the standard deviation significantly reduced to 8.1 cm. This value is slightly higher than those of traditional altimeters, which typically have a bias of ~7.0 cm. The results indicate that the InIRA is promising in providing a wide swath of SSH measurements. Moreover, we recommend that the InIRA retrieval algorithm should consider the two biases to improve SSH accuracy.

scholarly journals Research on Internal Solitary Wave Detection and Analysis Based on Interferometric Imaging Radar Altimeter Onboard the Tiangong-2 Space Laboratory

2021 ◽  
Vol 14 (1) ◽  
pp. 174
Author(s):  
Hao Zhang ◽  
Chenqing Fan ◽  
Junmin Meng ◽  
Shibao Li ◽  
Lina Sun
Keyword(s):  
Sea Surface ◽  
Height Anomaly ◽  
Small Scale ◽  
Interferometric Imaging ◽  
Radar Altimeter ◽  
Imaging Radar ◽  
Flight Direction ◽  
Sea Surface Height Anomaly ◽  
Geometric Relationship ◽  
Detection Effect

The Tiangong-2 space laboratory was launched by China on 15 September 2016, carrying the Interferometric Imaging Radar Altimeter (InIRA), the first of the latest generation of imaging altimeters that can perform imaging and acquire elevation information simultaneously. This paper analyzes the feasibility of using InIRA images to obtain two-dimensional characteristics of oceanic internal solitary waves (ISWs) and information about vertical sea surface fluctuations caused by the propagation of ISWs. The results show that InIRA demonstrates a relatively reliable ability to observe ISWs with high resolution and can identify the fine-scale features of ISWs of different forms. Furthermore, InIRA can observe centimeter-level changes in the Sea Surface Height Anomaly (SSHA) caused by ISWs. The geometric relationship between the sensor’s flight direction and the propagation direction of ISWs does not affect its detection effect. However, the swath width of InIRA is too narrow to fully capture ISW information, and the height accuracy of InIRA height product images is not insufficient to detect the height information of small-scale ISWs. These shortcomings need to be considered in the future development of imaging altimeters to increase their potential for detecting mesoscale phenomena in the ocean.

scholarly journals Preliminary Significant Wave Height Retrieval from Interferometric Imaging Radar Altimeter Aboard the Chinese Tiangong-2 Space Laboratory

2021 ◽  
Vol 13 (12) ◽  
pp. 2413
Author(s):  
Lin Ren ◽  
Jingsong Yang ◽  
Xiao Dong ◽  
Yongjun Jia ◽  
Yunhua Zhang
Keyword(s):  
Incidence Angle ◽  
Ocean Waves ◽  
Altimeter Data ◽  
Interferometric Imaging ◽  
Radar Altimeter ◽  
Significant Wave ◽  
Imaging Radar ◽  
Sea State Bias ◽  
Wave Heights ◽  
Low Incidence

The interferometric imaging radar altimeter (InIRA) aboard the Chinese Tiangong-2 space laboratory is the first spaceborne imaging radar working at low incidence angles. This study focuses on the retrieval of significant wave heights (SWHs) from InIRA data. The retrieved SWHs can be used for correcting the sea state bias of InIRA-derived sea surface heights and can supplement SWH products from other spaceborne sensors. First, we analyzed tilt, range bunching and velocity bunching wave modulations at low incidence angles, and we found clear dependencies between the SWH and two defined factors, range and azimuth integration, for ocean waves in the range and azimuth directions, respectively. These dependencies were further confirmed using InIRA measurements and collocated WaveWatch III (WW3) data. Then, an empirical orthogonal SWH model using the range and azimuth integration factors as model inputs was proposed. The model was segmented by the incidence angle, and the model coefficients were estimated by fitting the collocation at each incidence angle bin. Finally, the SWHs were retrieved from InIRA data using the proposed model. The retrievals were validated using both WW3 and altimeter (JASON2, JASON3, SARAL, and HY2A) SWHs. The validation with WW3 data shows a root mean square error (RMSE) of 0.43 m, while the average RMSE with all traditional altimeter data is 0.48 m. This indicates that the InIRA can be used to measure SWHs.

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