The presence of surface water on the canopy affects radar backscatter. However, its influence on the relationship between radar backscatter and crop biophysical parameters has not been investigated. The aim of this study was to quantify the influence of surface canopy water (SCW) on the relationship between L-band radar backscatter and biophysical variables of interest in agricultural monitoring. In this study, we investigated the effect of SCW on the relationship between co- and cross-polarized radar backscatter, cross ratios (VH/VV and HV/HH), and radar vegetation index (RVI) and dry biomass, vegetation water content (VWC), plant height and leaf area index (LAI). In addition, the effect of SCW on estimated vegetation optical depth (VOD) and its relationship with internal VWC was investigated. The analysis was based on data collected during a field experiment in Florida, USA in 2018. A corn field was scanned with a truck-mounted, fully polarimetric, L-band radar along with continuous monitoring of SCW (dew, interception) and soil moisture every 15 min for 58 days. In addition, pre-dawn destructive sampling was conducted to measure internal vegetation water content and dry biomass. Results showed that the presence of SCW can increase the radar backscatter up to 2 dB and this effect was lower for cross ratios (CRs) and RVI. The Spearman's rank correlations between radar observables and biophysical parameters were, on average, 0.2 higher for dry vegetation compared to wet vegetation. The estimated VOD from wet vegetation was generally higher than those from dry vegetation, which led to different fitting parameter (so-called b) values in the linear fit between VOD and VWC. The results presented here underscore the importance of considering the influence of SCW on the retrieval of biophysical variables of interest in agricultural monitoring. In particular, they highlight the importance of overpass time, and the impact that daily patterns in dew and interception can have on the retrieval of biophysical variables of interest.

冠层上地表水的存在会影响雷达后向散射。然而，其对雷达后向散射与作物生物物理参数之间关系的影响尚未得到研究。本研究的目的是量化地表冠层水 (SCW) 对 L 波段雷达反向散射与农业监测中感兴趣的生物物理变量之间关系的影响。在这项研究中，我们研究了 SCW 对同极化和交叉极化雷达后向散射、交叉比（VH/VV 和 HV/HH）、雷达植被指数 (RVI) 和干生物量、植被含水量 ( VWC)、株高和叶面积指数 (LAI)。此外，研究了 SCW 对估计植被光学深度 (VOD) 的影响及其与内部 VWC 的关系。 分钟 58 天。此外，还进行了黎明前破坏性采样以测量内部植被含水量和干生物量。结果表明，SCW 的存在可以将雷达后向散射增加至 2 dB，而这种影响对于交叉比 (CR) 和 RVI 的影响较小。与湿植被相比，干植被的雷达观测值和生物物理参数之间的 Spearman 等级相关性平均高 0.2。湿植被估计的VOD普遍高于干植被的VOD，这导致不同的拟合参数（所谓的b) VOD 和 VWC 之间线性拟合中的值。这里介绍的结果强调了考虑 SCW 对农业监测中感兴趣的生物物理变量检索的影响的重要性。他们特别强调了穿越时间的重要性，以及露水和拦截的日常模式可能对检索感兴趣的生物物理变量产生的影响。