Quikscat./ SeaWinds

Introduction

快速散射仪(快速放置在轨道上的仪器)于1999年6月推出,并于2009年11月进行操作。我们将该仪器称为Quikscat(或QSCAT),将其区分开于同一卫星平台上MIDORI的几乎相同的海风散射仪。2(美国科学家称为Adeos-II),从2002年12月到2003年12月开始运营。这些海风散射仪的主要任务是测量海面附近的风。它们对某些陆地和海冰应用也很有用。Seawinds仪器是一系列NASA散射仪中的第三个,该散射仪在Ku波段(即,近14GHz附近的频率)。1978年,第一个Ku-Band散射仪在Seasat上飞行.198年后,NSCAT于1996年8月在日本的Midori-1(Adeos-I)航天器上推出。欧洲人还将卫星散射仪飞行,在C波段运行(约。5 GHz)。其中两个名为ascat,目前正在运行。

SeaWinds scatterometers are essentially radars that transmit microwave pulses down to the Earth's surface and then measure the power that is returned back to the instrument. This "backscattered" power is related to surface roughness. For water surfaces, the surface roughness is highly correlated with the near-surface wind speed and direction. Hence, wind speed and direction at a height of 10 meters over the ocean surface are retrieved from measurements of the scatterometer's backscattered power.

Over many years, we developed and improved a Ku-band Geophysical Model Function (GMF). The current version is called Ku-2011. We use it to derive Wind Speed and Direction at 10-meter height over ice-free oceans from backscattered scatterometer signals. Our latest version of QuikScat data, V4, was released on April 28th, 2011 after a complete reprocessing using this new GMF. The goal of this activity was to improve wind speed retrievals, with special attention devoted to high winds.

Accurate observations of high winds over the oceans are important for analyses of phenomena that range from local (storms, cyclones) to global scales (air-sea exchanges, ocean circulation). However, satellite retrievals of high winds are challenging for two reasons. First, they are often contaminated by the presence of rain and it is difficult to separate the wind and rain signals in the retrievals. Second, validation data of winds greater than 20 m/s are scarce and therefore limit our understanding of the accuracy of the satellite-retrieved high winds.

数据处理

Quikscat.data underwent a final reprocessing after the instrument stopped functioning. We used our improved Ku-2011 GMF to produce the Version-4 (V4) data products. The GMF is used to derive Wind Speed and Direction at 10-meter height over ice-free oceans from backscattered scatterometer signals. Our goal is to provide high quality scatterometer wind speed retrievals for use in climate study.

When the methodology for QuikScat wind retrieval was developed at Remote Sensing Systems (Wentz and Smith, JGR 2001), validation data containing high winds were extremely limited. Extrapolations and assumptions were made for winds greater than 20 m/s. In the 10+ years since the launch of QuikScat, more validation data became available and it was easier to assess the quality of our Ku-2011 high winds.

使用Windsat数据作为校准目标,开发了新开发的KU-2011 GMF(Ricciardulli和Wentz,准备稿件)。RSS最近在Polarimetric风矢量检索方面取得了进步。Meissner和Wentz(IEEE TGARS,2009)开发了一种新的挡风玻璃算法,即使在雨中也有效,并使用NOAA飓风研究部门(HRD)DataSet在风暴条件下培训。万博网址是什么新的Quikscat模型功能,KU-2011,使用7年观察到的雷达反散射比(Sigma_0)与无雨风风向风检测合作。据信迎风检索是准确的,最高可达30米/秒。此外,Windsat能够精确地检测雨,并用于在开发散射计GMF时丢弃雨水的Quikscat Sigma_0。

Note that the QuikScat Ku-2011 (v4) wind speeds have been calibrated to rain-free WindSat data. Rain impacts scatterometer retrievals, on average resulting in a positive bias at low wind speeds (due to signal backscatter by rain drops) and a negative bias at high wind speeds (due to atmospheric attenuation of the signal). The wind direction is less affected by rain, except at high rain rates (above 8 mm/hr). QuikScat wind retrievals displayed on this website and provided in the data files on our ftp server exist in both rain-free and rainy areas. When possible, we provide a rain-rate estimate from one of our radiometers in addition to a stand-alone scatterometer rain flag. We advise Users to rely on both the scatterometer rain flag and the radiometer rain information within the file to remove rain-contaminated data from data processing. See the notes within the read routines provided for more information on how to access and apply the rain flags.

For the case of QuikScat, we use 4 satellite microwave radiometers (F13 SSMI, F14 SSMI, F15 SSMI, and TMI) to determine if rain is present at the location of the QuikScat observation. In addition, all available SSMIs are used to detect sea ice. Using the SSMI daily observations of sea ice, the scatterometer observations can be properly flagged so that reliable wind vectors can be obtained immediately next to the marginal ice zone. For the case of SeaWinds on ADEOS-II, the AMSR microwave radiometer on the same platform is used for rain and sea ice detection.

Changes one should expect to see in the v4 QuikScat data include:

  1. Decreased wind speeds for winds greater than 20 m/s
  2. Improved wind directions at very low (< 5 m/s) and high wind speeds (> 15 m/s)
  3. Better agreement between radiometer and scatterometer winds in typically high wind speed regions

数据文件的格式是一样的Quikscat.V4 and SeaWinds V3a data. The data file folder name is "bmaps_v04" and the file version designation has changed to "v4." All read routines (Fortran, IDL, MatLab and Python) will work on QuikScat v4 data as well as SeaWinds v3a data. More detailed information about the Ku-2011 GMF and QuikScat reprocessing can be found in the articleRicciardulli和Wentz(2015)and in the RSS technical reportReprocessed wind vectors QuikScat V04 with Ku-2011 Geophysical Model Function

RSS Scatterometer Data Products

We release both QuikScat (version-4) and SeaWinds on ADEOS-II (version-3a) data products. For both instruments, two types of products are available: 1) swath products which contain the data in one swath per file organized by swath rows perpendicular to satellite path or 2) gridded binary data files similar in many ways to those provided for RSS radiometer data.

测量 Definition
Surface Wind Speed

风speed 10 meters above the water surface, derived from surface roughness (wind stress), roughly equivalent to an 8 - 10 minute mean surface wind.

Surface Wind Direction

The angle of air movement (oceanographic convention).

Rain Info

Scatterometer data is less accurate in rain. Data products include a scatterometer derived rain flag, and co-located radiometer columnar rain rates.

Gridded Binary Files

我们通过将散射计轨道数据映射到0.25°纬度地球电网来生产每日和时间平均(3天,每周,每月)网格数据文件。

Gridded QuikScat and SeaWinds data are publicly available via FTP at:ftp://ftp.remss.com/qscat/bmaps_v04andftp://ftp.remss.com/seawinds/bmaps_v03

Folders and file names follow these conventions:

时间 目录路径 File Name
Daily [year]/[month]/ qscat_yyyymmddv4.gz

3-Day

[year]/[month]/ qscat_yyyymmddv4_3day.gz
Weekly weeks/ qscat_yyyymmddv4.gz
Monthly [year]/[month]/

qscat_yyyyymmv4.gz.

在[年],[月],“yyyy”,“mm”,“DD”和“V”代表:

[year] year folder Y2002,Y2003等
[month] 月文件夹 m01 (Jan), m02 (Feb) etc.
yyyy year 2002, 2003 etc.
mm 01 (Jan), 02 (Feb) etc.
dd day 01, 02, ... 31
v version 4

请注意,3天和每周文件在其结束时命名(包括第3或第7天)。

数据以单个字节值编码。每个数据文件包含一系列字节映射或BMAPS,每个字节映射或BMAPS在四分之一度分辨率下表示地球:1440 x 720字节。

Daily files字节阵列的大小1440 x 720 x 4 x 2(经度,纬度,参数,轨道段(升序或下降通行证))。4个参数是:UTC观察时间,海面风速,海面风向,以及雨旗/搭配辐射计雨组合值(see below). Two maps exist for each parameter: one of ascending orbit segments (local morning passes) and the other of descending orbit segments (local evening passes).

Dimension Represents Range
1440 longitude 0 to 360
720. latitude -90 to 90
4 parameter UTC时间,风速,风向,雨信息
2 orbital segment ascending passes, descending passes

因此,日常文件包含8个全局地图:
[ascending time, ascending speed, ascending direction, ascending rain info, descending time, descending speed, descending direction, descending rain info]

时间averaged files (3-day, weekly, monthly)are byte arrays of size 1440 x 720 x 3 (longitude, latitude, parameter). The 3 parameters are: Ocean Surface Wind Speed, Ocean Surface Wind Direction, and a Rain Flag / Collocated Radiometer Rain Rate combination value (see below).

Dimension Represents Range
1440 longitude 0 to 360
720. latitude -90 to 90
3 parameter wind speed, wind direction, rain info

时间averaged files contain 3 global maps: [wind speed, wind direction, rain info]

For averaged scatterometer data, wind speeds are scalar averaged, while wind directions are vector averaged. Thus, if daily observations record strong winds blowing in opposing directions, the scalar speed average will reflect the high average speed, and the vector direction average will point out the prevailing direction.

A time composite grid cell will contain data if a minimum number of observations exist:

Averaging Time Potential # observations Typical # observations Minimum # observations
3-Day 6 ~4 2
Weekly 14 ~10 5
Monthly ~60 ~45 20

Data on daily maps are overwritten at both the high latitudes where successive orbits cross and at the "seam" or region where the last orbit of the day overlaps the first orbit of the day.

中心的1440列的第一个单元格d 720 row map is at 0.125 E longitude and -89.875 latitude. The center of the second cell is 0.375 E longitude, -89.875 latitude.

The data values fall between 0 and 255. Specific values have been reserved:

0 to 250 = 有效的地球物理数据
251 = 不用于散射仪
252 = 不用于散射仪
253 = scatterometer observations exist, but are bad
254 = 没有散​​射仪观察
255 = 土地群众

The data values between 0 and 250 need to be scaled to obtain meaningful geophysical data. To scale the data:

TIME: either multiply by 6.0 to get 0 to 1440 minute of day UTC
or multiply by 0.1 to get 0.0 to 24.0 hour of day UTC
风Speed multiply by 0.2 to get 0.0 to 50.0 m/sec
风Direction multiply by 1.5 to get 0.0 to 360.0 degrees
Rain Flag extract first bit to get 0 = no rain; 1 = rain
Radiometer Rain extract bits 3 to 8 (x/2)-0.5 to get 0 to 31 km*mm/hr

风directions are provided in oceanographic convention. This means:

风s blowing North: 0° (or 360°)
风s blowing East: 90°
风s blowing South: 180°
风s blowing West: 270°

The Rain byte contains 3 pieces of information. Use bit extraction to obtain the following:

scatterometer rain flag
(bit 1)
0 = no rain
1 = rain
collocated radiometer flag
(bit 2)
0 = no radiometer data within 60 minutes
1 = radiometer data within 60 minutes
辐射计柱状雨率
(bits 3 - 8)
0 = no rain
1 = rain in adjacent cells
2 thru 63 = value/2 -0.5 rain rate in km*mm/hr)

文件以压缩形式存储。如果您的编程环境直接读取压缩文件,请在读取之前使用任何GZIP兼容的工具解压缩文件。

Read Routines

我们通过FTP提供Fortran,IDL,Matlab和Python读取例程ftp://ftp.remss.com/qscat/scatterometer_bmap_support.

The QuikScat and SeaWinds data file formats are identical. The read routines work for both QuikScat and SeaWinds datasets.

Missing Data

There are gaps within these data. Missing data generally affect Daily and 3-Day products, but can also reduce the number of observations in Weekly and Monthly averages.

When browsing imagery, the navigation may skip dates with no data, or you may see a blank map stating that no data are available for that time.

Binary data files for dates with completely missing data are not produced; they will be absent from our FTP server.

Data gaps are generally due to missing data upstream from our processing facility, such as the instrument being turned off. Occasionally, there are delays in obtaining and/or processing recently recorded data; beyond several weeks, it is unlikely that missing data will become available.

Official information on missing QuikScat and SeaWinds data can be found at:
http://podaac.jpl.nasa.gov/OceanWind/QuikSCAT/SeaWinds-QuikSCAT_KnownProblems/L2B_DataGaps

Rain Contamination

Rain is a well known problem affecting scatterometers. It tends to result in erroneous cross track vectors and/or unrealistically high speeds.

这是一个例子:

Quikscat.wind vectors 2006/02/14 evening passes Hawaii“src=

Note the rain contaminated data in the image. The scatterometer derived rain flag is used to draw the arrows grey instead of black. Collocated radiometer rain rates are also available in the data files. Scientists should use the rain flag and radiometer rain rates to help remove rain effects from the data files when doing research.

Regional Ice and Land Problems

Undetected winter sea ice affects the Sea of Asov (northern Black Sea) and the Northern Caspian Sea. The shrinking Aral Sea is affected year round by land exposure. Note that all of these areas are rain flagged.

Browse Images

Each daily, weekly, or monthly scatterometer image in our browse data section shows the wind speed and direction for a specific geographical region.

The daily browse images display the ascending and descending satellite passes separately. The approximate UTC time of each pass is labeled near the bottom of the image. The date of the data displayed is the UTC date when the data was collected(See the Map dates and Times section of the FAQs)。上升和下行段的观察时间在一天中交错。使用前一个和下一个按钮浏览日常通过段时,大约一半的地球将以时间顺序浏览;其他一半不会以时间顺序浏览。

A scale of 10 meter ocean surface wind speeds is located on each image and extends between zero and 45 m/s. Land regions are colored gray. Areas where scatterometer data are not available are black. For the daily maps, the black color includes areas where the satellite did not pass over and no data was collected, areas where data was collected but it was determined to be bad, coastal areas, and regions containing sea ice.

The browse images are produced from the same gridded data files available on our FTP server.

Swath Data Files

In addition to the gridded daily and time-averaged files, we release swath files only for scatterometer data. These files contain the measurements for one orbit of the satellite around the Earth. The data are organized by observation cells that are perpendicular to the direction the satellite travels. This makes the data grid at an angle to the standard lat/lon grid used in our other products.

轨道散射仪数据出版icly available via FTP at:ftp://ftp.remss.com/qscat/qscat_wind_vectors_v04/andftp://ftp.remss.com/seawinds/seawinds_wind_vectors/

The files are stored in directories based on orbit number (00000to09999, 01000to01999, 02000to02999, etc.). The file names have the form:

QuikSCAT: winvec_RRRRR_v04.gz
SeaWinds: winvec_RRRRR_v03.dat

where RRRRR is the five digit orbit number.

The orbital data file format is described at:ftp://ftp.ssmi.com/qscat/readme_scatterometer.txt

Date and time information for each orbit is located at:

QuikScat:

http://data.remss.com/qscat/qscat_info.txt.

SeaWinds:

http://data.remss.com/seawinds/seawinds_info.txt

The columns of the above files represent:

Orbit Number Number of good WVC rows Equatorial Crossing Date (UTC) 赤道交叉时间(UTC) 赤道过度经度

Orbit Period

Read routines are provided in Fortran, IDL, and Matlab at:ftp://ftp.remss.com/qscat/scatterometer_orbit_support/

Quikscat和Seawinds Swath文件格式是相同的。读取程序适用于Quikscat和Seawinds数据集。

Verification data to help ensure you are reading the data file correctly is at:ftp://ftp.remss.com/qscat/scatterometer_orbit_support/readme.txt

References

Mears, C.A., D.K.Smith, and F.J.Wentz, 1999,Development of a Rain Flag for QuikScat, technical report number 121999, Remote Sensing Systems, Santa Rosa, CA, 13 pp.

Ricciardulli,L.和F.J.Wentz,2011年,用KU-2011地球物理模型功能进行重新处理的Quikscat(V04)风矢量, technical report number 043011, Remote Sensing Systems, Santa Rosa, CA, 8pp.

Ricciardulli, L. and F.J. Wentz, 2015:A Scatterometer Geophysical Model Function for Climate-Quality Winds: QuikSCAT Ku-2011Journal of Atmospheric and Oceanic Technology, 32,1829-1846.

Wentz, F.J. and D.K. Smith, 1999,NSCAT观测中的14 GHz海洋归一化雷达截面的模型功能, Journal of Geophysical Research, 104(C5), 11499-11514.

相关数据集

The Ku-2011 GMF was provided to the Jet Propulsion Lab to be run on QuikScat data. The data available at the NASA PO.DAAC are very similar to those available at RSS. Different rain flagging and quality flagging are applied and a different gridding process is used to create the Level-3 wind products at JPL. The winds values themselves should contain only minor differences from the RSS data.

For more information and access to QuikScat data, seeJPL PO.DAAC

Acknowledgement

Quikscat和Seawinds数据是由NASA海洋矢量风科学团队提供资金的遥感系统。万博体育app网页注册由于NASA JPL提供用于创建这些产品的L2A数据文件。

How To Cite

Production of this data set could not have happened without support from NASA. We need you to be sure to cite these data when used in your publications so that we can demonstrate the value of this data set to the scientific community. Please include the following statement in the acknowledgement section of your paper:

“Quikscat.(or SeaWinds) data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Vector Winds Science Team. Data are available atwww.dj-hx.com。“

An official data citation for use in publications is given below. Insert the appropriate information in brackets.

For bytemap version of QuikSCAT data: Ricciardulli, L., F.J. Wentz, D.K. Smith, 2011: Remote Sensing Systems QuikSCAT Ku-2011 [indicate whether you used Daily, 3-Day, Weekly, or Monthly] Ocean Vector Winds on 0.25 deg grid, Version 4, [indicate subset if used]. Remote Sensing Systems, Santa Rosa, CA. Available online atwww.dj-hx.com/missions/qscat。[Accessed dd mmm yyyy].

对于轨道Quikscat数据:Ricciardulli,L.,F.J.Ventz,D.K.史密斯,2011年:遥感系万博体育app网页注册统Quikscat Ku-2011 [指示您是否使用每日,3天,每周或每月]轨道Swath海洋矢量风L2B,版本4,[表示子集]。万博体育app网页注册遥感系统,圣罗莎,加利福尼亚州。在线提供www.dj-hx.com/missions/qscat。[Accessed dd mmm yyyy].

SeaWinds ADEOS-II:温兹,F.J.位重度th, 2005: Remote Sensing Systems SeaWinds [indicate whether you used Daily, 3-Day, Weekly, or Monthly] Ocean Vector Winds on 0.25 deg grid, Version 3a, [indicate subset if used]. Remote Sensing Systems, Santa Rosa, CA. Available online atwww.dj-hx.com/missions/qscat。[Accessed dd mmm yyyy].