SLA and SSHA The difference between

One is sea level anomaly （Sea Level Anomaly）, One is sea level anomaly （Sea Surface Height Anomaly）.

The cause is https://www.mdpi.com/1424-8220/21/1/126/htm Such a passage in ：

Satellite altimeter can provide statistical information of surface eddies by detecting sea surface height anomalies (SSHA) [20], sea level anomalies (SLA) [21], or sea surface temperature (SST) [22]

After reading this paragraph, I began to doubt , SLA and SSHA Isn't it the same thing ?

Sea Level Anomaly(SLA)

according to http://www.tsgc.utexas.edu/topex/activities/elnino/sld005.html The explanation of ：

sea-level anomaly is the difference between the total sea-level and the average sea-level for this time of year. We look at anomalies because the total level measurement made by the altimeter varies from +/- 100 meters. Most of this is constant, though, and is due to the Earth’s gravity and the ocean circulation. Sea level variations caused by El Niño account for only 1% of the signals. If the constant part were not removed, the El Niño signal would not be observable.

Extract key points ：SLA It's this time of year Total sea level And Mean sea level Difference between .

according to https://coastwatch.noaa.gov/cw/stories/emilys-post/detecting-sea-level-anomalies-with-satellites.html That's what I'm saying ：

The sea surface is a dynamic mixture of bumps and dips resulting from a variety of factors including gravity, ocean currents and the rotation of the Earth. Scientists study variations in sea surface height using radar altimeters on satellites. These altimeters emit radar pulses that bounce off the ocean’s surface and are detected by a sensor on the satellite when they return. Sea surface height derived from satellite altimeters is accurate to within about 3-4 centimeters.
Anomalies in sea level can be identified by calculating the difference between the measured sea surface height and the average sea surface height. By studying sea level anomalies, scientists can improve understanding of ocean circulation patterns and improve forecasts of climatological events such as El Niño and La Niña.

Extract key points ：SLA Defined as Measured sea level And Average sea level Difference between .

Sea Surface Height Anomaly(SSHA)

according to https://sos.noaa.gov/catalog/datasets/sea-surface-height-anomaly-real-time/:

As anyone who has been on a boat knows, the ocean surface is not flat. It ripples and undulates due to wind and waves, rises with the tidal pull of the moon, expands and contracts as it heats and cools, and billows due to circulation patterns. Sea surface height anomaly data is able to characterize these small- and large-scale changes over weeks and years. An anomaly is the difference between the long-term average for different regions of the ocean and what is actually observed by satellites.

Extract key points ：SSHA It's from different parts of the ocean Long term average And Actual satellite observations Differences between .

according to https://www.e-education.psu.edu/earth107/node/1493

If you are interested in understanding climate change and you pay attention to in-depth news stories on the topic, you have no doubt frequently heard or read references to sea level and temperature anomalies. Anomaly data are being shared with greater regularity in the media these days, so it is important to understand what we mean by terms like sea surface temperature anomalies and sea surface height anomalies. An anomaly is an inconsistency or deviation from the norm, so images are created to show where change is taking place in the ocean in either a positive or negative trend when comparing to previous data. Sometimes this is referred to as Sea Surface Height Deviation data or SSHD. Sea surface height anomalies are calculated using data from satellite altimeters. Many years’ worth of thousands of measurements provide a historical mean sea surface height and the difference between the historical mean and the sea surface measurement for a particular date is called the sea surface height deviation. This can be calculated for points over the ocean surface, providing the data for the incredible maps we are seeing that show color-coded variations in sea surface across the globe and the changes in these measurements over time and space.

Extract key points ： Historical average And The difference between sea surface measurements on a particular date is called SSHA.

summary

http://www.altimetry.info/radar-altimetry-tutorial/data-flow/data-processing/reference-surfaces/ Referred to the ：

Sea Level Anomalies (SLA, also called SSHA, Sea Surface Height Anomalies) is the sea surface height with respect to a Mean Sea Surface or a Mean profile
So, SSH = (Altitude – Range – corrections) = geoid + ADT = MSS + SLA/SSHA = geoid + MDT + SLA/SSHA

Sea level anomaly （SLA, Also known as SSHA, Sea level anomaly ） Is the sea surface height relative to the average sea surface or average profile .
So the two are equal .

Calculation method

SSH： The satellite altimeter directly measures the sea surface elevation , Because the orbit is determined according to the reference ellipsoid , therefore SSH Is relative to the reference ellipsoid .
$$SSH=railAvenuehighdegree-highdegreemetermeasuringThe\; amount$$

MSS： According to a period of time (N) Of $SSH$ Calculate the mean sea surface $MS{S}_N$.
$$MS{S}_N=\frac{{\sum }_{k=1}^N(SS{H}_k)}{N}$$

The above two values are based on the reference ellipsoid (Ellipsoid of Reference) affirmatory , The calculation of relative geoid is more reasonable in practical application .

MDT： Average dynamic terrain (MDT) And the average sea level (MSS) similar , It's just calculated by geoid .
$$MD{T}_N=MS{S}_N-BigThe\; earthwateraccurateNoodles$$

ADT： Absolute dynamic terrain (ADT) And sea level (SSH) similar , It's just calculated by geoid .
$$ADT=SL{A}_N+MD{T}_N=SSH-MS{S}_N+MD{T}_N=SSH-BigThe\; earthwateraccurateNoodles$$

SLA： Sea level anomaly (SLA) Or abnormal sea level (SSHA) yes SSH or ADT The difference from its mean , Independent of datum .
$$SLA=SSHA=SSH-MS{S}_N=ADT-MD{T}_N$$