A CYGNSSâ Based Algorithm for the Detection of Inland Waterbodies

The Cyclone Global Navigation Satellite System (CYGNSS) is a new constellation of eight low Earth orbiting spacecrafts that receive both direct and reflected signals from GPS satellites. Coherent reflection of the GPS signal from standing water over land results in a high surface reflectivity signal in the CYGNSS data. An image processing algorithm is presented, which leverages the surface reflectivity signal to produce a watermask of inland waterbodies at 0.01° à 0.01° spatial resolution. The watermask is compared to handâ drawn maps of inland waterbodies, as well as to the MODIS watermask product. We find that the CYGNSS watermask provides accurate, timeâ varying maps that are able to resolve changes in lake and river position and extent. With CYGNSS’ short return time, watermasks can be generated using as little as half a month of data to produce nearâ realâ time maps of flooding events.Key PointsThe Cyclone Global Navigation Satellite System satellite constellation data are used to map inland water bodiesWe propose an algorithm to process this new data and create watermasks of rivers and lakesThe data combined with this method can be applied to monitor shortâ term events such as seasonal floodingPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153138/1/grl59790.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153138/2/grl59790_am.pd

Quantifying Seasonal and Diurnal Cycles of Solar‐Induced Fluorescence With a Novel Hyperspectral Imager

Solar-induced fluorescence (SIF) is a proxy of ecosystem photosynthesis that often scales linearly with gross primary productivity (GPP) at the canopy scale. However, the mechanistic relationship between GPP and SIF is still uncertain, especially at smaller temporal and spatial scales. We deployed a ultra-hyperspectral imager over two grassland sites in California throughout a soil moisture dry down. The imager has high spatial resolution that limits mixed pixels, enabling differentiation between plants and leaves within one scene. We find that imager SIF correlates well with diurnal changes in leaf-level physiology and gross primary productivity under well-watered conditions. These relationships deteriorate throughout the dry down event. Our results demonstrate an advancement in SIF imaging with new possibilities in remotely sensing plant canopies from the leaf to the ecosystem. These data can be used to resolve outstanding questions regarding SIF's meaning and usefulness in terrestrial ecosystem monitoring

Vegetation restoration in Northern China: A contrasted picture

China started a long- term effort to mitigate desertification and ensure the sustainability of its environment by implementing multiple large- scale national ecological restoration projects since 1978, but their success has been highly debated for a long time. Here, we estimated the change of vegetation fraction cover (VFC) in the Three- North Shelterbelt Programme (TNSP) region over the past three decades on the basis of the Normalized Difference Vegetation Index dataset from the Global Inventory Monitoring and Modeling System. We evaluate the national strategy of vegetation restoration in North China by comparing rainfall patterns, vegetation change, and national ecological restoration programs on the basis of the Global Meteorological Forcing Dataset and the China Forestry Statistical Yearbooks. We find that the western, central, and eastern parts of the TNSP region exhibited a distinct increase in vegetation coverage. The western region had the highest increase of annual precipitation, but this did not result in the highest VFC increase. We infer that ecological restoration activities are the factor leading to the observed increase in VFC in the eastern and central region compared with the western region. The low survival rate of planted trees in the forest of the TNSP region indicates that it is necessary to improve the mode of vegetation restoration to obtain optimal returns and avoid excessive investment. The success of new strategies, for example, natural restoration and quasinatural afforestation are promising as an alternative method. China’s experiences in reforestation will be very beneficial for other countries to promote land degradation mitigation and vegetation improvement in the arid and semiarid areas.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154888/1/ldr3314_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154888/2/ldr3314.pd

The Importance of Accounting for Landscape Position When Investigating Grasslands: A Multidisciplinary Characterisation of a California Coastal Grassland

Grasslands are one of the most common land-cover types, providing important ecosystem services globally, yet few studies have examined grassland critical-zone functioning throughout hillslopes. This study characterised a coastal grassland over a small hillslope at Point Reyes National Seashore, California, using multidisciplinary techniques, combining remotely-sensed, geophysical, plant, and soil measurements. Clustering techniques delineated the study area into four landscape zones, up-, mid-, and down-slope, and a bordering riparian ecotone, which had distinct environmental properties that varied spatially across the site, with depth, and time. Soil moisture increased with depth and down slope towards a bordering riparian zone, and co-varied with soil CO2 flux rates both spatially and temporally. This highlighted three distinct controls of soil moisture on soil respiration: CO2 fluxes were inhibited by high moisture content in the down-slope during the wet winter months, and converged across landscape positions in the dry summer months, while also displaying post-rain pulses. The normalised difference vegetation index (NDVI) ranged from 0.32 (September)–0.80 (April) and correlated positively with soil moisture and aboveground biomass, moving down slope. Yet, NDVI, aboveground biomass, and soil moisture were not correlated to soil organic carbon (SOC) content (0.4%–4.5%), which was highest in the mid-slope. The SOC content may instead be linked to shifts in dominant grassland species and their rhizosphere properties with landscape position. This multidisciplinary characterisation highlighted significant heterogeneity in grassland properties with landscape position, and demonstrated an approach that could be used to characterise other critical-zone environments on hillslopes

Adding our leaves: A communityâ wide perspective on research directions in ecohydrology

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154539/1/hyp13693.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154539/2/hyp13693_am.pd

Investigating dew deposition on leaves: effects on leaf water content, CO2, and remote sensing characterization

Dew deposition occurs in ecosystems worldwide, even in the driest deserts and in times of drought. Although some species absorb dew water directly via foliar up- take, a ubiquitous effect of dew on plant water balance is the interference of dew droplets with the leaf energy balance, which increases leaf albedo and emissivity and decreases leaf temperature through dew evaporation. Dew deposition frequency and amount are expected to be affected by changing environmental conditions, with un- known consequences for plant water stress and ecosystem carbon, water, and energy fluxes. In this dissertation, I seek to quantify the effect of dew deposition on leaves as well as the spatial extent of dew deposition, to provide an estimate of the effects of dew on water and carbon exchanges between vegetation and the atmosphere. In Chapter 2, I present a new protocol using a Picarro induction module coupled to a cavity ringdown spectrometer to obtain maps of the leaf water isotopes 18O and 2H. The technique is applied to Colocasia esculenta leaves, and I find that these leaves present a unique pattern of intra-leaf water isotopes with a strong radial enrichment and little longitudinal enrichment. In Chapter 3, I use the new method presented in Chapter 2 to study the effects of dew deposition on the water isotopes and water potential of C. esculenta. I discover that dew does not penetrate inside the leaves, but does impact their transpiration rate, helping them maintain a higher water potential. To better understand these results, I develop a dew deposition and leaf water, energy, and carbon balance model presented in Chapter 4. The model is compared to leaf wetness sensor data from the Blue Oak Ranch Reserve in California, and I find that dew deposition usually decreases both transpiration and carbon uptake. I conclude this dissertation by investigating the spatial extent of dew deposition events, which is currently largely unknown, by modeling the effects of dew droplets on leaves in active microwave remote sensing data