Gathering data over a dynamic topology is an issue in WSN. Radio links are unreliable due to changes in environmental conditions that induce drastic evolution of propagation conditions between nodes. This leads to a high dynamic connectivity and represents a big challenge for routing while maintaining the level of reliability required for the application. In this context, the synchronization of WSN nodes activity is a required condition to provide more efficient utilization of the radio interface and more energy saving. Researchers have proposed synchronization algorithms, mainly focused on synchronization accuracy and energy saving. However, these protocols are not well suited for WSN application requirements in harsh environments, where links are not always available nor are they bidirectional. This paper proposes a synchronization method that can meet the goal of dynamic topology and therefore can improve the data collection performance. The nodes use a hop by hop diffusion of a single message including a timestamp to synchronize their local clock. Our proposal uses a predetermined correction offset to adjust the receiver clock. We provide a technique that is based on (i) software defined radio observer nodes and on (ii) Texas Instrument CC430 based nodes to evaluate the degree of synchronization over a multi-hop topology. Several experimental measurements are taken to show the impact on the clock error of the distance (in number of hops) from a node to the sink.