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P-band Signals of Opportunity (SoOp) has great potential for remote sensing of root zone soil moisture (RZSM) from space. We have carried out a tower-based experiment with receivers to detect the reflected signals from the communications satellites at the Fraser Experimental Forests (FEFs), Colorado, in 2017. The measured reflectivity data at 260 MHz have a good correlation with in-soil moisture (SM) measurements. Retrieval of SM from the reflectivity data was also performed with results indicating accuracy of about 0.01 bias and 0.02 standard deviation (std) with respect to the average of SM in the upper 10 cm of soil. The experimental data and retrieval analyses lend support to the use of P-band SoOp for the remote sensing of SM. Our data also indicate the limitation of single frequency observations, suggesting the requirement of multiple frequencies to enable RZSM remote sensing because the surface SM plays a critical role on the change of reflectivity even at P-band frequencies.

Headwater forest ecosystems of the western U.S. generate a large portion of the dissolved organic matter (DOM) transported across North America. Land cover changes that alter forest structure and forest species composition affect the quantity and composition of DOM transferred to aquatic ecosystems. Clear-cut harvesting effects ~1% of the forest area of North America annually, leaving most forests in varying stages of successional regrowth, and the total area of old-growth forest decreasing. The consequences of this widespread management practice on watershed carbon cycling remain unknown. We investigated the role of land cover change from old-growth subalpine forest to lodgepole pine dominated second-growth on the character and reactivity of DOM hillslope exports. We evaluated inputs of DOM from litter leachates and export of DOM collected at the base of trenched hillslopes during a three-year period (2016-2018) at the Fraser Experimental Forest in northcentral Colorado, USA. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were higher in lateral subsurface flow draining old- versus secondary-growth forest. Fluorescence spectroscopy showed that the DOM exported from the old-growth forest was more heterogeneous and aromatic and that proteinaceous, microbially processed DOM components were more prevalent in the second-growth forest. Biological oxygen demand (BOD) assays revealed much lower microbial metabolism of both DOM inputs from litter leachate and subsurface exports from old-growth forest. Old-growth and second-growth forests are co-mingled in managed ecosystems, and our findings demonstrate that the influence of species composition on DOM inputs can affect the reactivity of DOM transferred from terrestrial to aquatic ecosystems.

A proof-of-concept experiment was carried out to demonstrate the feasibility of retrieving snow water equivalent (SWE) using P-band signals of opportunity. The fundamental observation is the change in the phase of the reflected waveforms as related to the change in SWE. Through theoretical modeling it was found that the change in SWE was approximately linearly dependent on the change in phase. This was verified by retrieving SWE data collected and processed from a tower-based experiment at Fraser, CO, USA. A linear regression was performed on measured phase and in situ SWE. The correlation was found to be 0.94 and root mean square deviation was found to be 7.5 mm.

The persistence and fall rate of snags (standing dead trees) generated during bark beetle outbreaks have consequences for the behavior, effects, and suppression of potential wildfires, hazard tree and timber salvage operations, wildlife habitat, and numerous ecosystem processes. However, post-beetle snagfall dynamics are poorly understood in most forest types. We tagged standing live and dead lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii), including beetle-killed pine snags following the peak of a recent mountain pine bark beetle outbreak in watersheds at the Fraser Experimental Forest in northcentral Colorado and sampled snagfall 10 and 12 years later. Bark beetle attacks began in 2003, peaked by 2006, and killed 78% of overstory lodgepole pine in 133 plots distributed across a range of stand and site conditions. Of those snags, only 17% fell between 2007 and 2018. Most snags broke at ground level, due to butt rot, and were oriented downhill. In contrast, snags that tipped up or snapped off above the ground were oriented with the prevailing winds. Equal numbers of snags fell singly and in multiple-tree groups, and equal numbers remained elevated rather than in contact with the ground. Lodgepole pine snagfall was 1.6-times higher on steep slopes (>40%) where dead pine density was higher, compared to flatter sites. Based on our findings and previous research, we estimate that one-half the beetle-killed lodgepole pine in high-elevation forests such as those at Fraser may fall within 15-20 yr of beetle infestation, but that some pine snags are likely to persist for decades longer. Post-outbreak snagfall dynamics create a multiple-decade legacy of bark beetle outbreaks that will persist longer in high-elevation compared to lower-elevation forests.

This paper shows results from a proof-of-concept tower experiment that computed phase and reflectivity from a reflected P-band signal. The change in phase of the reflected signal is related to SWE for dry snow and the rate of change of phase is directly correlated to frequency of observation. The effect of vegetation was also evaluated by using measurements from two towers: one with bare soil and one surrounded by small trees with heights of up to 3 meters. SWE has been retrieved from two sites with RMSD of 1.15-1.6 cm for different frequencies and sites. In addition, sensitivity in reflectivity measurement at 260 MHz due to changes in soil moisture was observed in summer 2018 data.