In order to build a long-term monitoring programme of marine macrophytes in the back-barrier island lagoons along the seaside of Virginia's Eastern Shore, an accurate rendition of Ulva thalli spectral properties was required. These properties included the unknown thallus reflectance, transmittance, and absorption and their expected variability. To provide that information, methods were developed to determine the visible (VIS) to near-infrared (NIR) spectral properties of thalli and epiphytes of the green macrophyte Ulva curvata. Based on the developed methodology, the study documented changes of VIS and NIR reflectance and transmittance and of the resultant thalli absorption. Replicate measurements confirmed these differences, indicating that thallus composition changed from summer to winter. Independent from the thalli spectral properties, surface epiphytes exhibited broadband VIS and NIR absorptions in summer and selective peaks in winter. As in the thalli, changes in the ephiphyte spectral properties indicated changes in composition. The capability to remotely detect occurrences of Ulva thalli was simulated by coupling water extinction (water turbidity) with the thallus spectral properties. Results of that simulation found seven submerged thalli maximized the surface reflectance enhancement.