science

Soil Moisture Active Passive

Soil Moisture Active Passive is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Soil Moisture Active Passive rather than just read about it. In short: Soil Moisture Active Passive (SMAP) is a NASA environmental monitoring satellite that measures soil moisture across the planet. It is designed to collect a global 'snapshot' of soil moisture every 2 to 3 days.

Key takeaways

Soil Moisture Active Passive belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Soil Moisture Active Passive to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Soil Moisture Active Passive from memory before moving on to harder problems.

Reference excerpt

Soil Moisture Active Passive (SMAP) is a NASA environmental monitoring satellite that measures soil moisture across the planet. It is designed to collect a global 'snapshot' of soil moisture every 2 to 3 days. With this frequency, changes from specific storms can be measured while also assessing impacts across seasons of the year. SMAP was launched on 31 January 2015. It was one of the first Earth observation satellites developed by NASA in response to the National Research Council's Decadal Survey. NASA invested US$916 million in the design, development, launch, and operations of the program. An early fault in a radar power supply limited the resolution of the radar data collected from 2015 onwards.

Mission overview SMAP provides measurements of the land surface soil moisture and freeze-thaw state with near-global revisit coverage in 2–3 days. SMAP surface measurements are coupled with hydrologic models to infer soil moisture conditions in the root zone. These measurements enable science applications users to:

Understand processes that link the terrestrial water, energy, and carbon cycles. Estimate global water and energy fluxes at the land surface. Quantify net carbon flux in boreal landscapes. Enhance weather and climate forecast skill. Develop improved flood prediction and drought monitoring capability. SMAP observations are acquired for a period of at least three years after launch, and the 81 kg of propellant that it carries should allow the mission to operate well beyond its design lifetime. A comprehensive validation, science, and the application program are implemented, and all data are publicly available through the NASA archive centers.

Status In August 2015, scientists completed their initial calibration of the two instruments on board, however, SMAP's radar stopped transmitting 7 July due to an anomaly that was investigated by a team at JPL. The team identified the anomaly to the power supply for the radar's high-power amplifier. On 2 September 2015, NASA announced that the amplifier failure meant that the radar could no longer return data. The science mission continues with data being returned only by the radiometer instrument. SMAP's prime mission ended in June 2018. The 2017 Earth Science senior review endorsed the SMAP mission for continued operations through 2020, and preliminarily, through 2023.

Measurement concept The SMAP observatory includes a dedicated spacecraft and instrument suite in a near-polar, Sun-synchronous orbit. The SMAP measurement system consists of a radiometer (passive) instrument and a synthetic-aperture radar (active) instrument operating with multiple polarizations in the L-band range. The combined active and passive measurement approach takes advantage of the spatial resolution of the radar and the sensing accuracy of the radiometer. The active and passive sensors provide coincident measurements of the surface-emission and backscatter. The instruments sense conditions in the top 5 cm of soil through moderate vegetation cover to yield globally mapped estimates of soil moisture and its freeze-thaw state. The spacecraft orbits Earth once every 98.5 minutes and repeats the same ground track every eight days.

Scientific payload The satellite carries two scientific instruments: a radar and a radiometer, that share a single feed and deployable 6 m reflector antenna system, built by Northrop Grumman, that rotates around the nadir axis making conical scans of the surface. The wide swath provides near-global revisit every 2–3 days.

SMAP system characteristics

Auxiliary Payloads Educational Launch of Nanosatellite X (ELaNa X), consisting of three Poly Picosatellite Orbital Deployers containing four CubeSats (three CubeSat missions), mounted on the second stage of the Delta II launch vehicle:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Soil Moisture Active Passive

Start with the simplest possible case. Write down what Soil Moisture Active Passive claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Soil Moisture Active Passive before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Soil Moisture Active Passive ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Soil Moisture Active Passive

In research: Soil Moisture Active Passive appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Soil Moisture Active Passive in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Soil Moisture Active Passive is common in secondary-school and first-year university syllabi. It links to neighbouring topics Earth observation satellites of the United States, Jet Propulsion Laboratory satellites, NASA satellites, so understanding it makes those chapters shorter.
In everyday life: Look for Soil Moisture Active Passive outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Soil Moisture Active Passive” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Soil Moisture Active Passive in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Soil Moisture Active Passive means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Soil Moisture Active Passive out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Soil Moisture Active Passive in simple terms?

Why does Soil Moisture Active Passive matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Soil Moisture Active Passive?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Soil Moisture Active Passive.