{'fraction_non_alphanumeric': 0.04855923159018143, 'fraction_numerical': 0.012806830309498399, 'mean_word_length': 5.377551020408164, 'pattern_counts': {'":': 0, '<': 22, '<?xml version=': 0, '>': 22, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Relative Calibration Using Natural Terrestrial Targets: A Preparation Towards Oceansat-2 Scatterometer

Scatterometer instruments transmit a series of microwave pulses and measure the returned echo to determine the normalized radar cross section (σ<sup>0</sup>) over the target to derive the near-ocean-surface wind vector. Accuracy of the derived wind vector over the data sparse oceans therefore depends on the accuracy of σ<sup>0</sup> measurement. For this purpose, accurate calibration of the scatterometer is required. As a preparation toward calibration of the Oceansat-2 mission, of the Indian Space Research Organisation, a relative calibration technique has been proposed in this study by selecting homogeneous areas over the globe with isotropic radar response and temporally stable signature of σ<sup>0</sup>. For this purpose, the daily averaged σ<sup>0</sup> and Level-2A (L2A) σ<sup>0</sup> measurements of the QuikSCAT scatterometer have been used. Analyzing the monthly mean and standard deviation in σ<sup>0</sup> for the period of 2005-2006, several regions are chosen which have a quasi-isotropic radar response and minimal temporal variation in σ<sup>0</sup>. The analysis shows that the selected areas over Antarctica and Greenland with permanent ice covers have temporally stable signatures of σ<sup>0</sup>. The regions like the Amazon forests and parts of Australia also show high temporal stability of σ<sup>0</sup> but greater standard deviation than the snow-covered areas. The QuikSCAT L2A data have also been used to study the day-night variation and azimuthal dependence of the σ<sup>0</sup> over these targets. The present work demonstrated that quasi-uniform natural sites such as Sahara, Amazon forest, Kutch, Greenland region, and Antarctica region, covering wide dynamic range of σ<sup>0</sup>, can be used for the purpose of calibration.