Shape of particle backscattering in the North Pacific Ocean: the χ factor
Xiaodong Zhang, Lianbo Hu, Deric J. Gray, Yuanheng Xiong
Abstract
Volume scattering functions were measured using two instruments in waters near the Ocean Station Papa (50°N 145°W) and show consistency in estimating the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>χ</mml:mi> </mml:math> factor attributable to particles ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:mrow> </mml:math> ). While <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:mrow> </mml:math> in the study area exhibits a limited variability, it could vary significantly when compared with data obtained in various parts of the global oceans. The global comparison also confirms that the minimal variation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:mrow> </mml:math> is at scattering angles near 120°. With an uncertainty of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo><</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>10</mml:mn> </mml:mrow> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:mrow> </mml:math> can be assumed as spectrally independent. For backscatter sensors with wide field of view (FOV), the averaging of scattering within the FOV reduces the values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>p</mml:mi> </mml:msub> </mml:mrow> </mml:math> needed to compute the backscattering coefficient by up to 20% at angles <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo><</mml:mo> </mml:mrow> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>130</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> .