Relasphone—Mobile and Participative In Situ Forest Biomass Measurements Supporting Satellite Image Mapping

Abstract

Due to the high cost of traditional forest plot measurements, the availability of up-to-date in situ forest inventory data has been a bottleneck for remote sensing image analysis in support of the important global forest biomass mapping. Capitalizing on the proliferation of smartphones, citizen science is a promising approach to increase spatial and temporal coverages of in situ forest observations in a cost-effective way. Digital cameras can be used as a relascope device to measure basal area, a forest density variable that is closely related to biomass. In this paper, we present the Relasphone mobile application with extensive accuracy assessment in two mixed forest sites from different biomes. Basal area measurements in Finland (boreal zone) were in good agreement with reference forest inventory plot data on pine (R 2 = 0.75, RMSE = 5.33 m 2 /ha), spruce (R 2 = 0.75, RMSE = 6.73 m 2 /ha) and birch (R 2 = 0.71, RMSE = 4.98 m 2 /ha), with total relative RMSE(%) = 29.66%. In Durango, Mexico (temperate zone), Relasphone stem volume measurements were best for pine (R 2 = 0.88, RMSE = 32.46 m 3 /ha) and total stem volume (R 2 = 0.87, RMSE = 35.21 m 3 /ha). Relasphone data were then successfully utilized as the only reference data in combination with optical satellite images to produce biomass maps. The Relasphone concept has been validated for future use by citizens in other locations.

Assessing Precision in Conventional Field Measurements of Individual Tree Attributes

“…The reported accuracy in dbh measurements has varied from 0.8 cm to 1.6 cm (standard error) with the laser-relascope [47], and from 0.88 cm to 1.43 cm with laser-dendrometers [48,49]. With camera-based systems, the accuracies have varied from 0.7 cm to 2.3 cm [30,[50][51][52]. Terrestrial laser scanning (TLS) is also used for dbh measurements.…”

Feasibility of Google Tango and Kinect for Crowdsourcing Forestry Information

“…In forestry, crowdsourcing has been applied in assessing condition of city trees [15,16], even though some questions concerning the reliability of such has been raised [17]. By utilizing applications potentially useable in crowdsourcing scenarios, a basal area accuracy of 5 m 2 /ha [18], RMSE for basal area of 19.7-29.3% [19] and DBH root mean squared error of less than 7 cm [20] have been achieved.…”

The Role of Citizen Science in Earth Observation

“…[27] Phenology Online *** ** * -+ ** P, C Laso Bayas et al [23] Land Cover Field-based ** ** * -+ * S, F, P, C Molinier el al. [25] Forestry Field-based *** *** --+ * S, P Salk et al [24] Land Cover Online *** -** --* C Wallace el al. [26] Phenology Field-based * -*** + -* P *** high ** medium * low + applies -does not apply; S = cost savings, F = higher frequency, P = potential Cal/Val dataset, C = complements RS data or traditional in situ observations.…”

“…The article by Molinier et al [25] presents the Relasphone mobile application (version 1.5, VTT Technical Research Centre of Finland, Espoo, Finland), developed to collect in situ data for forest inventories, namely, basal area and tree species, height, diameter and age, among other data of interest. These data are expensive to obtain with traditional methods, and thus data collection is usually limited to only a small number of samples.…”