Soil moisture measurement for agriculture

Chapter 2. Whilst infrastructure projects have often focused on improving the supply of water for agriculture, there has been much less focus on managing or reducing the agricultural water demand. The net effect of increasing supply, without managing demand, is that agricultural water (and energy) consumption increases, without necessarily increasing food production. Improved agricultural Water Use Efficiency (WUE) can help address this issue, as well as contributing to reducing the pressures on water resources (NITI Aayog 2019). This chapter outlines how recent improvements in large area measurement of soil moisture and the availability of high-resolution Soil Moisture Deficit information at a fine scale can provide actionable guidance to farmers. Practical methods, demonstrated in farm pilot studies, to manage irrigation demand are discussed, along with considerations of efficient irrigation methods, with the objective of improving WUE

The Indian COSMOS Network (ICON): validating L-band remote sensing and modelled soil moisture data products

Availability of global satellite based Soil Moisture (SM) data has promoted the emergence of many applications in climate studies, agricultural water resource management and hydrology. In this context, validation of the global data set is of substance. Remote sensing measurements which are representative of an area covering 100 m2 to tens of km2 rarely match with in situ SM measurements at point scale due to scale difference. In this paper we present the new Indian Cosmic Ray Network (ICON) and compare it’s data with remotely sensed SM at different depths. ICON is the first network in India of the kind. It is operational since 2016 and consist of seven sites equipped with the COSMOS instrument. This instrument is based on the Cosmic Ray Neutron Probe (CRNP) technique which uses non-invasive neutron counts as a measure of soil moisture. It provides in situ measurements over an area with a radius of 150–250 m. This intermediate scale soil moisture is of interest for the validation of satellite SM. We compare the COSMOS derived soil moisture to surface soil moisture (SSM) and root zone soil moisture (RZSM) derived from SMOS, SMAP and GLDAS_Noah. The comparison with surface soil moisture products yield that the SMAP_L4_SSM showed best performance over all the sites with correlation (R) values ranging from 0.76 to 0.90. RZSM on the other hand from all products showed lesser performances. RZSM for GLDAS and SMAP_L4 products show that the results are better for the top layer R = 0.75 to 0.89 and 0.75 to 0.90 respectively than the deeper layers R = 0.26 to 0.92 and 0.6 to 0.8 respectively in all sites in India. The ICON network will be a useful tool for the calibration and validation activities for future SM missions like the NASA-ISRO Synthetic Aperture Radar (NISAR)

An analytical delay model for RLC interconnects

We develop an analytical delay model based on rst and second moments to incorporate inductance e ects into the delay estimate for interconnection lines. Delay estimates using our analytical model are within 15 % of SPICE-computed delay across a wide range of interconnect parameter values. We also extend our delay model for estimation of source-sink delays in arbitrary interconnect trees. For the small tree topology considered, we observe improvements of at least 18 % in the accuracy of delay estimates when compared to the Elmore model (which isindependent of inductance), even though our estimates are as easy to compute as Elmore delay. The speedup of delay estimation via our analytical model is several orders of magnitude when compared to a simulation methodology such as SPICE. 1

New efficient algorithms for computing effective capacitance

recent 0.25µm high-end microprocessor project confirm the accuracy of We describe a novel iterationless approach for computing the effective our new methods. capacitance of an interconnect load at a driving gate output. Our new approach is considerably faster than previous methods for computing 2 Review of Gate Load Models effective capacitance, with little or no loss of accuracy. Thus, the ap- With narrower deep-submicron interconnect geometries, the resistive proach is suitable within the analysis loop for performance-driven itera- component of the gate load is comparable to or larger than the gate tive layout optimization. After reviewing previous gate load models and output resistance: the gate does not “see ” all of the capacitance load-effective capacitance approximations, we separately derive our method ing since the metal resistance “shields ” some capacitance. The resis-for the cases of step and ramp waveform at the gate output, and note ontance shielding effect is very significant for deep-submicron technologoing extensions for the case of complex gates (e.g., channel-connected gies. For example, if we increase the interconnect resistance of the components). Experimental results using the new effective capacitance load and keep the gate output resistance constant, the total gate delay approach show that our resulting delay estimates are quite accurate – at the output will decrease since the interconnect resistance will tend to within 15 % of HSPICE-computed delays on data corresponding to an shield some of the load capacitance. In this case, while the total gate 0.25µm microprocessor design. delay decreases, the increase in interconnect resistance would increase the interconnect propagation delay.

Analysis of RC Interconnections Under Ramp Input”, ACM Trans. on Design Automation of Electronic Systems

We give new methods for calculating the time-domain response for a finite-length distributed RC line that is stimulated by a ramp input. The following are our contributions. First, we obtain the solution of the diffusion equation for a semiinfinite distributed RC line with ramp input. We then present a general and, in the limit, exact approach to compute the time-domain response for finite-length RC lines under ramp input by summing distinct diffusions starting at either end of the line. Next, we obtain analytical expressions for the finite time-domain voltage response for an open-ended finite RC line and for a finite RC line with capacitive load. The delay estimates using this method are very close to SPICE-computed delays. Finally, we present a general recursive equation for computing the higher-order diffusion components due to reflections at the source and load ends. Future work extends our method to response computations in general interconnection trees by modeling both reflection and transmission coefficients at discontinuities

Delay analysis of coupled transmission lines

In this paper, we analyze coupled transmission lines and obtain a relationship between the moments of the coupled transfer functions. We then derive expressions for the first and second moments of the coupledtransfer function which can be used to computethe response and threshold delays under various input excitations. We can compute the interconnectdelay under parasitic coupling effects by using the analytic delay formulas given in [8, 9] for step and ramp inputs. We also present the analysis to compute the general kth moment for the coupled interconnect lines.